Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudfl ow,

By David A. John, James J. Rytuba, Roger P. Ashley, Richard J. Blakely, James W. Vallance, Grant R. Newport, and Gary R. Heinemeyer

Prepared for the Society of Economic Geologists Field Trip, November 6, 2003

Bulletin 2217

U.S. Department of the Interior U.S. Geological Survey Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

By David A. John, James J. Rytuba, Roger P. Ashley, Richard J. Blakely, James W. Vallance, Grant R. Newport, and Gary R. Heinemeyer

Bulletin 2217

U.S. Department of the Interior U.S. Geological Survey 1 U.S. Department of the Interior Gale A. Norton, Secretary

U.S. Geological Survey Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

U.S. Geological Survey, Reston, Virginia: 2003

Electronic copies of this publication are available online at http://geopubs.wr.usgs.gov/bulletin/b2217/

Additional USGS publications can be found online at http://geology.usgs.gov/products.html

For more information about the USGS and its products: Telephone: 1-888-ASK-USGS (1–888–275–8747) World Wide Web: http://www.usgs.gov/

Published in the Western Region, Menlo Park, California

Manuscript approved for publication October 25, 2003

2 Contents

Introduction ...... 1 Road log from Enumclaw to the White River Altered Area and the Osceola Mudflow along the lower White River, Washington ...... 2 Part 1: The White River Altered Area ...... 3 Geology of the White River Altered Area ...... 3 Economic Geology of the White River Altered Area—Historical Perspective ...... 4 Hydrothermal Alteration and Mineralization in the White River Area...... 4 Geophysical Framework of the White River Altered Area...... 6 Geochemical Exploration Studies of the White River Altered Area...... 7 Stop 1: Superior (Ash Grove) Silica Quarry...... 9 Stop 2: Taugow...... 10 Stop 3: Scatter Creek (James Hardie) Silica Quarry...... 10 Part 2: The Osceola Mudflow in the Lower White River ...... 11 General Features of the Osceola Mudflow ...... 11 Hydrothermal Alteration in the Osceola Mudflow ...... 12 Stop 4: Osceola Mudflow near Greenwater...... 13 Stop 5: Osceola Mudflow in the Corliss Gravel Quarry...... 13 References...... 13

Figures

1. Map showing location of the Western Cascades and High Cascades arcs and associated mineral deposits, northwestern ...... 16 2. Map showing areas inundated by Holocene debris flows from ...... 17 3. Photograph of vuggy silica alteration in the Scatter Creek (James Hardie) silica quarry ..... 17 4. Geologic map of the White River area, showing field trip stops...... 18 5. Heterolithic breccia () in the Fifes Peak Formation...... 20 6. Finely bedded tuffs from small outcrop about 0.5 km north of the Superior quarry...... 20 7. Silicified flow-banded dacite showing large flow fold...... 20 8. Map showing distribution of hydrothermal alteration in the White River area ...... 21 9. Photo of leached phenocrysts in vuggy silica alteration in the Scatter Creek quarry...... 22 10. Photo showing sharp contact between vuggy silica alteration and advanced argillic alteration in the Scatter Creek quarry ...... 22 11. Schematic model for high-sulfidation gold deposits, showing zoning of hydrothermal alteration assemblages and ore types ...... 23

12. Log ƒO2-pH diagram showing fluid relations forming vuggy silica alteration ...... 23 13. Aeromagnetic anomalies of the White River altered area and surrounding regions...... 24 14. Cross sections of IP surveys across the White River altered area ...... 25 15. Geophysical anomalies of the White River altered area and surrounding regions...... 26 16. Ground magnetic studies of the White River altered area...... 27 17. Ground magnetic profile across White River altered zone...... 28 18. View of the Superior (Ash Grove) quarry from Taugow...... 28 19. Generalized geologic map of the Superior quarry...... 29 20. Gray vuggy silica rock with abundant voids after phenocrysts in andesite flow...... 30 21. Photographs of sulfide minerals in vuggy silica from the Superior quarry ...... 30 22. Enargite filling funnel-shaped void in white chalcedonic silica in the Superior quarry ...... 30

III 23. Tan chalcedony replacing relict flow and devitrification layers in dacite flow in the Superior quarry...... 31 24. Massive tan chalcedony cut by hydrothermal breccias with sulfides in gray areas in the Superior quarry...... 31 25. Felsic porphyry dike in the Superior quarry...... 31 26. Hydrothermal breccia with clasts of early stage white chalcedony in tan to gray chalcedony with sulfides in gray areas in the Superior quarry ...... 32 27. Sulfide-bearing hydrothermal breccia developed in massive tan silicified rock in the Superior quarry...... 32 28. Massive tan silicified rock cut by stockwork of sulfide-bearing gray chalcedony in the Superior quarry...... 32 29. Brecciated siliceous hydrothermal sedimentary rocks in the Superior quarry ...... 33 30. Fault breccia with clay-supported fragments that contains high gold content (1.7 ppm) in the Superior quarry...... 33 31. North-striking fault with red clay gouge developed in massive vuggy silica rock ...... 33 32. Red to brown smectite clay zone developed from alteration of bedded tuff ...... 34 33. Taugow from the Superior quarry ...... 34 34. Knob of alunitic alteration on Taugow...... 34 35. Leached silicified tuff breccia with relict pyroclastic textures exposed in road cut near top of Taugow ...... 35 36. Narrow fine-grained silicic dike cutting silicified tuff breccia near top of Taugow...... 35 37. Blocks of vuggy silica alteration in hydrothermal breccia near top of Taugow...... 35 38. Generalized geologic map of the Scatter Creek quarry...... 36 39. Stockpile of sized silica at Scatter Creek quarry...... 37 40. Gray vuggy silica rock cut by white quartz and chalcedony veins and hydrothermal breccias in the Scatter Creek quarry...... 37 41. Voids developed in porphyritic andesite after leached plagioclase and pyroxene phenocrysts by acid hydrothermal fluids leaving a residual ground mass of silica...... 37 42. Northeast-trending rib of orangish-brown vuggy silica alteration in the Scatter Creek quarry ...... 38 43. “Clay hole” of propylitic alteration in Scatter Creek quarry ...... 38 44. Oxidation in the Scatter Creek quarry...... 39 45. Vuggy silica cut by white chalcedonic hydrothermal breccia and veins in the Scatter Creek quarry ...... 39 46. Vuggy silica cut by hydrothermal breccias in the Scatter Creek quarry...... 40 47. Fracture in vuggy silica filled with late stage hydrothermal red clay in the Scatter Creek quarry ...... 40 48. White outcrops of leached rock formed in the near-surface steam-heated zone in the Scatter Creek quarry ...... 41 49. Map showing distribution of the Osceola Mudflow and Paradise lahar ...... 41 50. Dark-gray clay-pyrite rich matrix of the Osceola Mudflow...... 42 51. Typical outcrop of the Osceola Mudflow along the White River near Greenwater, Washington ...... 42 52. Typical smectite-pyrite alteration of andesite clast in the Osceola Mudflow...... 42 53. Back-scattered SEM image of smectite alteration of andesite clast in the Osceola Mudflow..... 43 54. Back-scattered SEM image of smectite-pyrite alteration of andesite clast in the Osceola Mudflow...... 43 55. Back-scattered SEM image of advanced argillic altered clast in Osceola Mudflow ...... 43 56. Back-scattered SEM image of advanced argillic altered clast in Osceola Mudflow ...... 44 57. Back-scattered SEM image of intergrown alunite and kaolinite in advanced argillic altered clast in the Osceola Mudflow ...... 44

IV 58. Back-scattered SEM image of alunite containing P-rich domains in advanced argillic altered clast in the Osceola Mudflow...... 44 59. Back-scattered SEM image of vug-filling anhydrite/gypsum and fluorite in advanced argillic altered clast in the Osceola Mudflow ...... 45 60. Schematic diagram showing formation of normal zoning by incremental deposition model for mass flow deposits ...... 45 61. Exposure of Osceola Mudflow overlying well bedded late Pleistocene glacial-fluvial deposits in the Corliss quarry...... 46 62. Partly charred trees protruding from the Osceola Mudflow in the Corliss quarry ...... 46 63. Base of the Osceola Mudflow in the Corliss quarry...... 46 Tables

1. Mineral assemblages in the White River altered area ...... 47 2. Types of silicic alteration in the White River altered area...... 48

V Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

By David A. John1, James J. Rytuba1, Roger P. Ashley1, Richard J. Blakely1, James W. Vallance2, Grant R. Newport3, and Gary R. Heinemeyer4

Introduction for silica and advanced argillic alteration has been prospected for alunite. Clay-filled fractures and sulfide-rich, fine-grained sedimentary rocks of hydrothermal origin locally are enriched The Cenozoic Cascades arcs of southwestern Washington in precious metals. Many hydrothermal features common in are the product of long-lived, but discontinuous, magmatism high-sulfidation gold-silver deposits and in advanced argil- beginning in the Eocene and continuing to the present (for lic alteration zones overlying porphyry copper deposits (for example, Christiansen and Yeats, 1992). This magmatism is example, Gustafson and Hunt, 1975; Hedenquist and others, the result of subduction of oceanic crust beneath the North 2000; Sillitoe, 2000) are exposed, although no economic base American continent. The magmatic rocks are divided into or precious metal mineralized rock has been discovered to two subparallel, north-trending continental-margin arcs, the date. The afternoon will be spent examining two exposures Eocene to Pliocene Western Cascades, and the Quaternary of the Osceola Mudflow along the White River. The Osceola High Cascades, which overlies, and is east of, the Western Mudflow contains abundant clasts of altered Quaternary rocks Cascades (fig. 1). Both arcs are calc-alkaline and are char- from Mount Rainier that show various types of hydrothermal acterized by voluminous mafic lava flows (mostly basalt to alteration and hydrothermal features. The mudflow matrix basaltic andesite compositions) and scattered large stratovolca- contains abundant hydrothermal clay minerals that added noes of mafic andesite to dacite compositions. Silicic volca- cohesiveness to the debris flow and helped allow it to travel nism is relatively uncommon. Quartz diorite to granite plutons much farther down valley than other, noncohesive debris flows are exposed in more deeply eroded parts of the Western from Mount Rainier (Crandell, 1971; Vallance and Scott, Cascades Arc (for example, Mount Rainier area and just north 1997). of Mt. St. Helens, fig. 1). The White River altered area is the subject of ongoing Hydrothermal alteration is widespread in both Tertiary studies by geoscientists from Weyerhaeuser Company and the and Quaternary igneous rocks of the Cascades arcs. Most U.S. Geological Survey (USGS). The generalized descrip- alteration in the Tertiary Western Cascades Arc resulted from tions of the geology, geophysics, alteration, and mineralization hydrothermal systems associated with small plutons, some of presented here represent the preliminary results of this study which formed porphyry copper and related deposits, including (Ashley and others, 2003). Additional field, geochemical, geo- copper-rich breccia pipes, polymetallic veins, and epithermal chronologic, and geophysical studies are underway. gold-silver deposits (fig. 1). Hydrothermal alteration also The Osceola Mudflow and other Holocene debris flows is present on many Quaternary stratovolcanoes of the High from Mount Rainier also are the subject of ongoing studies by Cascades Arc. On some High Cascades volcanoes, this altera- the USGS (for example, Breit and others, 2003; John and oth- tion resulted in severely weakened volcanic edifices that were ers, 2003; Plumlee and others, 2003, Sisson and others, 2003; susceptible to failure and catastrophic landslides. Most notable Vallance and others, 2003). Studies of hydrothermal alteration is the sector collapse of the northeast side of Mount Rainier in the Osceola Mudflow are being used to better understand that occurred about 5,600 yr. B.P. This collapse resulted in fossil hydrothermal systems on Mount Rainier and potential formation of the clay-rich Osceola Mudflow that traveled 120 hazards associated with this alteration. km down valley from Mount Rainier to covering more than 200 km2 (fig. 2). This field trip examines several styles and features of Overview of Field Trip and Field Guidebook hydrothermal alteration related to Cenozoic magmatism in the Cascades arcs. The morning of the trip will examine the This one-day trip has five stops, the first three are in the White River altered area, which includes high-level altera- White River altered area and latter two are in the Osceola tion related to a large, early Miocene magmatic-hydrothermal Mudflow (fig. 4). The five stops are: Stop 1—Superior silica system exposed about 10 km east of Enumclaw, Washington quarry, Ash Grove Cement Co.; Stop 2—Taugow breccia pipe; (figs. 1 and 3). Here, vuggy silica alteration is being quarried Stop 3—Scatter Creek silica quarry, James Hardie Building Products, Inc.; Stop 4—Osceola Mudflow near Greenwater; and Stop 5—Osceola Mudflow in the Corliss gravel quarry. 1 U.S. Geological Survey, Menlo Park, California. The first part of the guidebook contains a short road log 2U.S.Geological Survey, Vancouver, Washington. 3Weyerhauser Company, Federal Way, Washington. from Enumclaw through the White River altered area and 4Tucson, Arizona. along the White River to Greenwater.

1 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

The second part of the guidebook contains short chapters 7.1 Denny-Renton quarry on left. The quarry produced on the geologic setting of the White River altered area, the small amounts of silica prior to 1936 and after World history of economic geology in the area, general features of War II. More recently, the quarry has been backfilled hydrothermal alteration in the area, geophysical features of the by large blocks of silicified rock from the Superior altered area, and geochemistry of the alteration. These chap- (Ash Grove) quarry. ters are followed by detailed descriptions of the three field trip 7.4 Intersection, turn right toward the Superior quarry. stops in the White River altered area. The third part of the guidebook describes general features 8.0 Stop 1, Superior (Ash Grove) quarry. See detailed of the Osceola Mudflow and a preliminary study of hydrothermal description of the Superior quarry below. After the alteration in the mudflow. These sections are followed detailed tour of the quarry, turn around and exit. Taugow is descriptions of the two field trip stops in the Osceola Mudflow. visible at 12:00 when leaving quarry. 8.6 Intersection; turn right onto main road. Acknowledgments 8.8 Intersection; stay to right. 9.7 Intersection; turn left (hard left uphill). We want to thank Weyerhaeuser Company for access to 10.2 Optional stop to collect alunite. Good exposures of the Superior and Scatter Creek silica quarries, Scott Corliss lapilli tuff breccia containing abundant pale pink of Corliss Resources for access to the Corliss gravel quarry, alunite crystals on both sides of road. Denis Johnson of Weyerhaeuser for computer graphics, Steve Box for unpublished field data, and Robert Oscarson for help 10.3 Intersection, turn right. with the SEM. Reviews of the field guide by Ted Theodore 10.8 Coarse alunitic tuff breccia cut by hydrothermal brec- and Don Singer were very helpful. cias in low road cuts. Fragments in tuff breccia are various types of andesites. 10.85 Stop 2, Taugow. See detailed description of this stop Road Log from Enumclaw to the White below. The rocky knob to west with clump of trees is silicified andesitic lapilli tuff. Superior quarry is River Altered Zone and the Osceola in middle distance to the left (west-southwest) of Mudflow along the Lower White River, this knob. Examine this knobby outcrop and the low roadcuts back down the road. Washington On clear days, a 360° panorama of the White River altered area and the surrounding region is visible Elapsed from the top of Taugow: glacier-covered Mount Rain- mileage ier is at S. 20° E. The peak to due south is composed of 0.0 Intersection of Washington State Highways 164 and the Pleistocene basalt of Canyon Creek that uncon- 410. Reset odometer to 0.0. Turn left onto Washing- formably overlies the late Oligocene to early Miocene ton State Highway 410 and travel east. Fifes Peak Formation. The hill below in the middle distance is entirely altered; the outcrops are silicified 1.1 Gravel quarry on left. and significant amounts of silicified rock have been 1.5 Corliss gravel quarry on left. We will return to the delineated for possible future mining for silica. Corliss quarry this afternoon for Stop 5 to look at To the west beyond the silicified knob is the the Osceola Mudflow. The quarry produces sand and lower White River Valley with buttes composed of gravel from glacial kame terraces that were banked Fifes Peak Formation in the distance. Enumclaw lies against the west edge of the during in the lowlands beyond these buttes. Pleistocene glaciation. The skyline to the north and northeast with the 3.5 The “410” aggregate quarry on left. Andesitic lava radio towers is Grass Mountain, which was mapped flows of the Fifes Peak Formation are quarried for by Tabor and others (2000) as the Oligocene Ohana- crushed rock. pecosh Formation. The slope in the middle distance is porphyritic andesite of Fifes Peak Formation. This area 5.0 Mud Mountain Road on right. Road runs to the Mud marks the northern edge of the White River hydrother- Mountain Dam, a U.S. Army Corps of Engineers flood mal system. Strands of the White River Fault Zone control dam. The dam was authorized by Congress in trend west-northwest through the terrain between this 1936 after the White River flooded in December 1933 slope and Grass Mountain, juxtaposing the Fifes Peak devastating Tacoma and other parts of the Puget Sound Formation against the older Ohanapecosh Formation. lowlands. World War II delayed construction of the To the east is the White River Valley and the dam, which was finally completed in 1948. Naches Pass area is on the skyline. To the southeast 6.4 Intersection with Scatter Creek Road on left. Turn left across White River, the altered area continues. The and pass through gate onto private timber company cliff with the trees on top bounding a clear cut, trend- lands. ing downhill to the west, is another major silicified

2 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

zone. Exploration for alunite in the 1940s was in an altered volcanic rocks, one covering about 20 km2 on the north area to the left of this silicified zone. side of the White River, and a second covering about 3 km2 on Clearwater Creek is at S. 45° E. The Fifes Peak the south side of White River. Alteration is likely continuous Formation is exposed in Clearwater Creek canyon. between these areas beneath surficial deposits in the White The upland areas east of Clearwater Creek are occu- River Valley. pied by rhyolite and rhyolite tuff units of Clear West Bedrock in the area has been included in the Fifes Peak Peak. These rocks have been interpreted as being Formation by Tabor and others (2000) and McCulla (1986) related to a caldera (McCulla, 1986). (fig. 4). It consists mainly of porphyritic basaltic andesite and Turn vehicles around and drive back down road. andesite flows and breccias (fig. 5). The typical porphyritic 11.9 Intersection with main road. Turn left. rock contains plagioclase, clinopyroxene, and orthopyrox- ene phenocrysts. Many outcrops in the altered area north of 12.6 Stop 3, entrance to Scatter Creek (James Hardie) the White River show relict fragmental textures, and locally quarry. See detailed description of the quarry below. show compaction or eutaxitic structures, suggesting that the After tour of the Scatter Creek quarry, turn original rocks were tuffs and tuff breccias (fig. 6). These vehicles around and drive back down main road rocks are shown as a separate subunit of the Fifes Peak by toward the paved road. Tabor and others (2000) (fig. 4). This subunit was interpreted 16.0 Intersection with Washington Highway 410. Turn left by McCulla (1986) as outflow facies rhyolite tuff related to up the White River Valley. For next 10 miles, the road a caldera located about 10 km to the southeast in the Clear- passes in and out of Fifes Peak Formation andesites water River drainage. Detailed mapping in the altered area and glacial deposits. Hydrothermal alteration related has shown that this unit also may contain rhyolite or dacite to the White River hydrothermal system ends after flows, possibly part of a local flow-dome complex (fig. 7; G. about 3.5 miles. Heinemeyer and G. Newport, unpub. data, 2003), and sparse 27.0 Cross the White River Fault Zone, a major NW–strik- felsic dikes. ing high-angle fault that juxtaposes Fifes Peak The age range of the Fifes Peak Formation in the Sno- Formation andesite on the south against well-bedded qualmie Pass 30 x 60 minute quadrangle is about 20–24 Ma andesite to dacite breccia, volcaniclastic sedimen- (Tabor and others, 2000). Only two samples of the Fifes Peak tary rocks, and locally abundant altered basalt and andesite in the vicinity of lower White River have been dated andesite flows of the somewhat older Ohanapecosh isotopically, yielding K–Ar ages of 24.1±0.8 and about 21.5 Formation. Ma (Tabor and others, 2000; Weyerhaeuser Co., unpub. data, 1994). Intracaldera rhyolite to the south at Clear West Peak, 27.5 Greenwater. which is thought to be related to the extracaldera unit, has 28.5 Fire station on left side of road. been dated at about 22 Ma (Mattinson,1977). 28.8 Gravel road on right side of road to private houses. The White River Fault Zone is a major fault zone that Park along the highway just past the gravel road. crosses the Cascade Range in the vicinity of Naches Pass, then Stop 4, Osceola Mudflow along White River. Find follows the Greenwater and White Rivers in a west-northwest- a trail parallel to the highway and walk about 50 feet erly direction, passing 2 to 3 km north of the northern part of west. Find a place to drop off the high terrace down the altered area (fig. 4; Tabor and others, 2000). Rocks north to river level. Continue west about 100 feet to the of the White River Fault are mapped as part of the Ohana- outcrop right at river level. See detailed description of pecosh Formation by Tabor and others (2000). The Ohana- the outcrop below. pecosh consists of highly altered, well-bedded andesite to Return to vehicles, Turn around and drive back dacite breccia, volcaniclastic sedimentary rocks, and locally down Highway 410 toward Enumclaw. abundant altered basalt and andesite flows. It is somewhat older than the Fifes Peak, and it is thought to unconformably 41.6 Scatter Creek Road on right. Continue west on High- underlie the Fifes Peak Formation. Tabor and others (2000) way 410 to the Corliss quarry. also show a fault in the Clearwater River valley that strikes 46.5 Stop 5, Osceola Mudflow in the Corliss gravel north-northwest into the altered area (figs. 4 and 8). quarry. See detailed description of the Corliss quarry Quaternary surficial deposits are extensive in the lower below. End of road log. White River area. They include glacial deposits and mudflows from Mount Rainier. Between the two altered areas, the bot- tom of the valley of the White River is relatively flat and more than 1 km wide; it broadens westward to a width of 7 to 8 Part 1: The White River Altered Area km. This low-lying area is underlain by glacial deposits of the Vashon stage of Fraser glaciation. Although most exposures Geology of the White River Altered Area of glacial material in this area have been mapped as undivided Vashon drift (Tabor and others, 2000), till, kame terrace, and The White River altered area is located in the western recessional outwash deposits have been recognized. Cascade Range 8 to 15 km east-southeast of Enumclaw, Alpine glacial deposits, including till and outwash, Washington. It comprises two adjacent areas of intensely locally mantle bedrock on the sides of the White River Valley.

3 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Tabor and others (2000) show a relatively large area of such cal data. Preliminary results of this work and other on-going deposits occupying the drainage area of Scatter Creek to the geophysical and geochemical investigations are described in northwest of the larger altered area. this guide. The low-lying glacial deposits are mantled by laharic deposits originating from Mount Rainier. The Osceola Mud- flow (Crandell, 1971; Vallance and Scott, 1997) is the most Hydrothermal Alteration and Mineralization in extensive of these deposits. the White River Area Introduction Economic Geology of the White River Altered The White River altered area consists of intensely altered Area—Historical Perspective rocks that are exposed across an area covering about 25 km2 on both sides of the White River near its confluence with the According to Callaghan (1940) and Huntting (1955), Clearwater River (fig. 8). Most alteration is exposed on the silicified rock of the White River area was prospected for northwest side of the White River, and this guidebook focuses gold in the late 1800s. Two adits, one about 100 m long, were on a reconnaissance study of hydrothermal alteration in this driven near the White River just south of the Superior quarry. area. The White River altered area displays many characteris- A stamp mill was erected in about 1890 to mill the ore, but it tic features that are associated with quartz-alunite (high-sul- was soon abandoned. Assays were said to range from about fidation) gold deposits (for example, Ransome, 1909; Steven 0.03 to 0.07 oz Au/ton. In the late 1920s, alunite-bearing rock, and Ratte, 1960; Arribas, 1995; Hedenquist and others, 2000) initially assumed to be clay, was exposed by the White River and with the upper parts of porphyry copper-gold deposits (for Logging Company in cuts made in the course of constructing example, Sillitoe, 2000). a logging railway. Alunite was identified in the early 1930s, and subsequently the Kalunite Company of Salt Lake City, Utah, explored the area for alunite by drilling and trenching. Previous and Present Studies Some public lands within the altered area were explored by the McCulla (1986) described general alteration features Washington Division of Mines and Geology. Exploration done and showed the distribution of some key alteration minerals in the late 1930s and early 1940s yielded estimated reserves of in the White River altered area. Reconnaissance mapping by 1,140,000 tons of rock containing more than 20 percent alunite Weyerhaeuser Co. (1996) distinguished areas of argillic and (Livingston, 1971; Kelly and others, 1956). advanced argillic alteration and silicification from unaltered The only commodity exploited to date in the White River and propylitized rocks (fig. 8). They performed a limited altered area is silica. Although not mentioned in reports on number of x-ray diffraction (XRD) analyses confirming their the alunite exploration, silica was produced by the Denny- alteration types. The USGS has analyzed about 100 samples Renton Clay and Coal Co. from a small quarry near the west widely distributed across the north side of the White River edge of the northern altered area (Denny-Renton quarry, fig. altered area using infrared spectrometry (PIMA) (fig. 8, table 8) some time before 1936 (Glover, 1936; Valentine, 1960). 1). The sample density is inadequate to define regional-scale After World War II, Manufacturers Mineral Co. operated this alteration zoning, if present, but analysis of these samples quarry. Another small quarry located just north of Washing- confirms the general types of alteration and identifies some ton Highway 410 in Section 7 (T.19 N., R. 8 E.) on the south previously unknown alteration minerals. Additional petro- flank of Quarry Hill (fig. 8) was operated by Superior Port- graphic, XRD, geochemical, and geochronological studies of land Cement, Inc. in 1948 (Valentine, 1960, described therein these samples are underway. as in R. 7 E.). This quarry also is known informally as the ASARCO quarry, because reportedly silica from this site was used as flux by the ASARCO smelter at Tacoma. Description of Hydrothermal Alteration Recent quarry operations include the Superior pit, oper- ated by Ash Grove Cement Co., which was started in 1987, Hydrothermal alteration on the north side of the White and the Scatter Creek quarry operated by James Hardie Build- River altered area consists of two large bodies of massive ing Products, Inc., started in 1999 (fig. 8). Features of these silica ± alunite that presently are being mined for silica, as active quarries are described in detail in this field guide. well as numerous other bodies of silica (fig. 8). The silica Weyerhaeuser Company began exploration for base and bodies consist of vuggy silica alteration of andesite lava flows precious metals in the White River hydrothermal system in and breccias, pyroclastic rocks, and hydrothermal breccias that 1986. Work done to date includes geochemical analysis of have been overprinted by subsequent stages of hydrothermal cuttings from many blast holes in and around the active silica brecciation and chalcedonic silica veins and vug fillings (table pits, rotary drill holes to average depths of about 125 m in 2). The silica bodies define two large zones of intense altera- the large areas of silicification, a soil geochemical survey of tion where alkalis and alumina have been leached leaving a selected areas both north and south of White River, periodic residual rock with greater than 95 weight percent silica. One detailing mapping of the Superior and Scatter Creek silica silica body trends east-west and extends for about 5.5 km and quarries, isotopic dating, and recently, an IP survey north another trends northeast for about 7 km. Bordering the zones of White River and modeling of existing USGS geophysi- of silica are areas of low relief and limited outcrops of argillic

4 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington and advanced argillic alteration containing kaolinite, dickite, Structural Control of Acid-Sulfate Alteration alunite, illite, and locally, pyrophyllite (fig. 8). The distribution and geochemistry of the silica bodies have been documented Residual vuggy silica alteration typically is structurally during exploration, development, and mining of the silica bod- controlled (for example, Ransome, 1909; Steven and Ratte, ies. There is less information on the extent and geochemistry 1960). Elongation of the silica bodies in the northern part of the argillic and advanced argillic alteration that borders the of the White River altered area (fig. 8) suggests that major silica bodies. The size, continuity, and intensity of silicifica- structural controls are east-northeast- and east-striking faults. tion and advanced argillic alteration are comparable to other In addition, some suggestion is present that silicification along large acid-sulfate systems that are associated with high-sul- the edges of the White River hydrothermal system may follow fidation gold-silver deposits and with porphyry copper-gold minor radial structures developed outward from hydrothermal mineralization. and perhaps local volcanic vents. However, few structures The acid-sulfate alteration formed in andesite flows and controlling vuggy silica alteration are obvious in either the breccias assigned to the Oligocene to early Miocene Fifes Superior or Scatter Creek quarries. On the north side of the Peak Formation, and in the Superior quarry, an intermediate Scatter Creek quarry, a prominent silicified ridge of vuggy composition (dacite?) flow or flow dome (fig. 7). The latter silica alteration strikes N. 10° W. The ridge is comprised of possibly is correlative with the rhyolite of Clear West Peak, vuggy silica alteration developed in pyroclastic rocks and and bedded tuffs and tuff breccias assigned as a rhyodacite porphyritic andesites of the Fifes Peak Formation, which tuff member of the Fifes Peak Formation by Tabor and others are cut by numerous, irregular hydrothermal breccia bodies. (2000) (figs. 4, 6, and 8). Because of the intensity of the acid Another narrow silicified rib of vuggy silica strikes N. 70° E. leaching, the original composition and primary textures of and dips 75° NW. The vuggy silica alteration here is bordered many volcanic rocks are not discernable. In the Superior and by narrow zones of alunitic and illitic alteration (fig. 10; also Scatter Creek quarries, vuggy silica alteration locally contains see section on the Scatter Creek quarry below). numerous small vugs with morphology typical of plagioclase and pyroxene phenocrysts in the andesite flows in the Fifes Peak Formation (fig. 9). Other areas consist of massive, fine- Age of Hydrothermal Alteration grained silica that may represent alteration of aphyric glassy Isotopic ages of alunite from the advanced argillic altera- volcanic rock. In the southwest part of the Superior quarry, a tion range from 20.4 to 23.5 Ma (McCulla, 1986; Weyer- flow-banded volcanic rock of intermediate composition has haeuser Co., 1996). The youngest age, 20.4±0.1 Ma, is from relict devitrification layers and contains xenoliths of another Cady Hill (fig. 8) and determined by Ar–Ar methods. Alunite intermediate composition volcanic rock. Sparse felsic dikes from a drill hole near the Superior quarry has a K–Ar age of are present in both the Scatter Creek and Superior quarries and 21.0±0.9 Ma, and alunite from Taugow has a K-Ar age of on Taugow. 22.3±0.9 Ma. Alunite from south of the White River (Bridge The advanced argillic alteration consists of massive Camp alunite, fig. 8) has a K–Ar age of 23.5±1.1 Ma. We are zones of residual silica bordered by alteration assemblages in the process of dating several additional alunite samples using composed of kaolinite, dickite, alunite, pyrophyllite, and Ar–Ar techniques. It is likely that the entire area of advanced pyrite (fig. 8, table 1). Illite-, montmorillonite-, and chlorite- argillic alteration formed from the same hydrothermal system. rich argillic and propylitic alteration is present outside the zone of advanced argillic alteration, but is poorly documented because of poor exposure. Residual vuggy silica alteration Inferred Environment of Hydrothermal Alteration commonly displays relict voids developed after phenocrysts and (or) pumice clasts. Enargite and pyrite are present within The advanced argillic alteration at White River formed the vuggy silica rock and in hydrothermal breccias, but for from disproportionation of magmatic SO2 to H2S and H2SO4 the most part, the sulfide minerals are oxidized and leached during condensation of a magmatic vapor plume (Rye and at present levels of exposure in the mines. Casts of pyrite others, 1992; Stoffregen, 1987; Arribas, 1995), as indicated by also contribute to the vuggy texture of the residual silica. In mineral assemblages (table 1), types of silicic alteration (table the Scatter Creek quarry, fine-grained hematite replaces the 2), and reconnaissance stable isotope data in McCulla (1986). sulfide minerals and gives the rock a dark gray color. Locally The acid condensate leaches most major and minor elements in the silica deposits, voids are not present and the silica is from the host rock leaving residual silica and forming zones of massive with little remnant texture. The massive nature of the alunite and kaolinite (or pyrophyllite at higher temperatures), silica may in part reflect the massive nature of the original illite, montmorillonite, and propylitic alteration progressively rock, as well as late-stage deposition of hydrothermal silica outward from the residual silica core. This alteration zoning that filled voids and fractures. Late-stage deposition of hydro- results from progressive neutralization and increasing pH of thermal silica and sulfide minerals locally shows sedimentary acidic magmatic-hydrothermal fluids due to rock buffering textures and horizontal banding (see section on the Superior outward from fluid conduits (figs. 10 to 12; also see description quarry below). The silica ranges from white chalcedonic of the Scatter Creek quarry). In this magmatic-hydrothermal silica to black chalcedony with darker colors reflecting the environment, transport of rare earth and other elements, such as presence of sulfide minerals and (or) hematite replacement of F, Cl, Ti, and P, leads to formation of minerals, such as zunyite, sulfide minerals. woodhouseite, svanbergite, crandellite, and rutile-anatase, that

5 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington may occur in the zone of alunite-kaolinite alteration. Elevated Widely spaced tie lines were flown in the east-west direction concentrations of F, as much as 0.75 weight percent, and TiO2, to facilitate data processing. as much as 3.8 weight percent, are present in the advanced Magnetic anomalies (fig. 13A) surrounding the White argillic alteration at the Superior quarry (fine-grained rutile River altered area display short-wavelength, high-amplitude crystals have been observed in the Superior quarry and on Cady patterns characteristic of unmetamorphosed volcanic ter-

Hill). Zunyite (Al13Si 5O20 (OH)16 F2Cl) has been identified rane (fig. 13B). The most pronounced magnetic anomalies by PIMA in one sample collected about 500 m northwest of are associated with volcanic rocks of the Miocene Fifes Peak the Scatter Creek quarry (fig. 8). Gallium concentrations are Formation and the Oligocene Ohanapecosh Formation in the elevated in alunite-kaolinite alteration peripheral to the zone northeastern and south-central parts of the study area. The of vuggy silica alteration in the Superior quarry, as much as west-northwest-striking White River Fault Zone, which brings 101 ppm, and depleted in vuggy silica alteration, less than 0.5 these two formations into contact, is evident in the aeromag- ppm. The Ga enrichment is typical of that present in zones of netic anomalies, and other anomalies with similar WNW trend alunitic alteration formed in the magmatic-hydrothermal envi- are related to mapped structures. Aeromagnetic anomalies (fig. ronment in other high sulfidation gold-silver deposits (Rytuba 13A) also display north-northeast trends, possibly indicat- and others, in press). High Au concentrations, as much as 1.7 ing faults antithetic to the White River Fault Zone, although ppm, are present in fault and fracture zones that formed late in no ENE–striking faults are mapped in the region (fig. 13B)). the hydrothermal system. The Au–enriched fault breccias and The White River altered area is located near the intersection fractures are filled with red clay consisting of montmorillonite of WNW– and ENE–trending anomalies, perhaps reflecting ± dickite and earthy hematite. structural control on the evolution of the hydrothermal system. The acid-sulfate alteration in the White River area is Magnetic anomalies in the immediate vicinity of the inferred to have formed at shallow depths beneath the paleo- White River altered area may have implications for mineral surface on the basis of sedimentary textures formed during resource evaluations. A small magnetic high (label A, fig. late-stage hydrothermal alteration and types of silicic altera- 13A) corresponds closely with intense acid-sulfate altera- tion (fig. 11, table 2). Hydrothermal depositional textures and tion, exposed silica bodies, and a large shallow zone of very the presence of steam-heated acid-leached rocks in the Scatter high resistivity and high chargeability zone at depth (fig. 14; Creek quarry (see section on the Scatter Creek quarry below) Weyerhaeuser Co., 2003). It seems unlikely that altered rocks indicate that the present exposures reflect the upper part of the exposed at the surface contribute significantly to the positive hydrothermal system. Similarly, bedded hydrothermal sedi- magnetic anomaly. The anomaly may reflect an underlying ments in the Superior quarry also indicate very shallow levels intrusive body possibly related to the hydrothermal evolution of the exposure of the hydrothermal system (see section on of the White River altered area. the Superior quarry below). Alteration features and possible A broad, polygonal-shaped magnetic low (label B, base- or precious-metal mineralization at greater depths are fig. 13A) is also difficult to explain on the basis of regional unknown, because exploration drilling has been limited to geologic mapping. Sharp gradients around the margins of the shallow (average 125-m-deep), vertical drill holes, mostly magnetic low suggest that its source lies near the topographic within the silica quarries. surface. The anomaly is underlain by Fifes Peak Formation, which includes rhyolite and rhyodacite tuff. Such rocks com- monly have low magnetizations, but exposures of these rocks Geophysical Framework of the White River elsewhere in the study area do not show pronounced aeromag- Altered Area netic lows. The zone of intense acid sulfate alteration overlaps the magnetic low on its southeastern margin (fig. 13), sug- Regional Magnetic Anomalies gesting that the anomaly may be caused by the destruction of magnetite during alteration of volcanic rocks. If so, the lateral Volcanic rocks are typically magnetic and produce dis- extent of the magnetic low would permit mapping the lateral tinctive magnetic anomalies. Therefore, intense and pervasive extent of intense alteration. Both anomalies A and B were hydrothermal alteration of volcanic rocks and the concomitant investigated in the field during the summer of 2003, and those destruction of magnetic minerals sometimes produce negative preliminary results are discussed below. anomalies in low-altitude magnetic measurements. Thus, an investigation was initiated to examine existing aeromagnetic data from, and conduct ground-magnetic measurements in, the Regional Gravity Anomalies White River altered area. Figure 15 shows a comparison of aeromagnetic and Figure 13 shows aeromagnetic anomalies surrounding gravity anomalies over the White River altered area. Such the White River altered area. These data were acquired by the comparisons are facilitated by first converting aeromagnetic USGS in 1997 as part of ongoing earthquake hazard investiga- anomalies to pseudogravity anomalies (fig. 15A), a linear tions of the Puget Lowland (Blakely and others, 1999). Flight filtering operation that in effect replaces magnetization with lines were flown north-south at a nominal altitude of 250 m density in one-to-one proportions (Blakely, 1995). The lack above terrain, or as low as safely possible. Lines were spaced of any obvious correlation between pseudogravity (fig. 15A) 400 m apart over the Puget Lowland, but were spaced 800 m and observed gravity (fig. 15B) throughout the White River over outlying regions, including the White River altered area. study area demonstrates that variations in magnetization are

6 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington not obviously linked with variations in density, a common that magnetite-destructive alteration lies entirely above these observation in volcanic terrane. depths. Drill holes did not extend to these depths, however. A notable exception is present directly over the altered The pronounced aeromagnetic low to the west of the area. Gravity stations are rather sparse in this region, however, silicified zone (label B, fig. 13A) remains problematic. Several precluding detailed comparisons of gravity anomalies with explanations are possible. (1) The anomaly is located over a geology and aeromagnetic anomalies. Nonetheless, a small region of relatively flat and subdued topography bounded on positive gravity anomaly does lie partially within the altered the north, south, and east by higher terrain. The possibility that zone, approximately corresponding with the positive aeromag- the negative anomaly is caused by variations in aircraft altitude netic anomaly (label A, fig. 13A and 15A), thus adding support and terrain effects was considered, but modeling experiments to the existence of a relatively shallow intrusion possibly using digital elevation models indicate that this is not the associated with the White River hydrothermal system. case. (2) The anomaly may reflect a subsurface extension of hydrothermally altered volcanic rocks, but the lack of correla- Field Investigations tion between ground-magnetic and aeromagnetic anomalies on the one hand and susceptibility measurements and silicified Detailed field studies were conducted during the summer rock on the other makes that conclusion difficult to defend. (3) of 2003 to investigate the near-surface expression of aero- The magnetic low may be caused by a thick basin filled with magnetic anomalies in the White River altered area. Stud- relatively nonmagnetic glacial deposits. Such a basin should ies included three ground-magnetic transects walked along produce a negative gravity anomaly as well, but gravity mea- logging roads using a portable cesium-vapor magnetometer. surements, although sparse, show a slight positive anomaly. A base station was established on Taugow to simultaneously (4) The magnetic low may be caused by reversely magnetized measure diurnal and transient fields, which were subsequently volcanic rocks that erupted during a time of reversed magnetic subtracted from the ground-magnetic profiles. In addition, the polarity. Future field studies and magnetic modeling experi- ground-magnetic measurements were judiciously edited to ments are planned to evaluate these alternative explanations. remove cultural artifacts and magnetometer dropouts. Mag- netic susceptibility measurements also were made at 27 sites inside and outside the altered zone using a hand-held suscepti- Geochemical Exploration Studies of the White bility meter. River Altered Area As expected, susceptibility measurements (fig. 16A) show a clear correlation between extraordinarily weak magnetiza- Weyerhaeuser Company work has focused on geologic tion and the exposed zone of intense silicification. This cor- mapping and surface exploration sampling programs in relation transcends the original rock type, as altered andesite specific areas, including working mine faces, and on detailed flows are just as low in susceptibility as altered pyroclastic geochemical analysis of drill holes. Geochemical sampling has rocks. The only exception to the correlation is a single site targeted zones of intense silicification, hydrothermal breccias, (label X, fig. 16A), where high susceptibility was found inside areas of outcrop, and locations with soil sample anomalies. the altered zone. This site is located within a quarry excavated Additionally, several, large reconnaissance-scale soil sample into a laterally restricted fresh basalt or andesite of apparent surveys have been completed. Areas with the highest sample Fifes Peak age. density and most geochemical data include the Superior quarry Figure 16B shows magnetic intensity measured along one area, the Scatter Creek quarry area, the Taugow area, the of the ground-magnetic transects. As expected, the general Quarry Hill area, and altered areas south of the White River aspects of the ground-magnetic profile agree with the aero- (fig. 8). magnetic data. Most notable, the western edge of the aeromag- Many trace elements in the White River altered area netic high agrees closely with a sharp gradient in the ground- are elevated to varying degrees in the most siliceous areas. magnetic profile. Surprisingly, the dramatic destruction of Anomalous elements include Au, As, Cu, Sb, Bi, Te, Pb, Zn, magnetic minerals, evident in susceptibility measurements Mo, Hg and Se. Statistical analysis of geochemical data and (fig. 16A), is not obviously reflected in either the aeromagnetic field observations suggest that in the Superior quarry hill area or ground-magnetic data. This suggests that the aeromagnetic there may be two primary geochemical associations—Cu- and ground-magnetic anomalies originate from sources below As±Te, probably related to enargite deposition in vuggy silica, the zone of alteration. and Bi-Sb-Te-Au-Mo-As related to hydrothermal veins and Although the source of the magnetic high is clearly not breccias. the altered volcanic rocks exposed at the surface, the source Experience has shown that sampling of the highly probably lies at relatively shallow depth. This is evident from leached surface exposures rarely produces geochemical results the sharp magnetic gradient on the ground-magnetic profile representative of the original trace element composition. In (arrow, fig. 17). Using a simple graphical technique (Blakely, fact, samples from surface outcrops commonly are devoid of 1995, p. 238–239), it is estimated that the source of this gradi- anomalous concentrations. Sampling of subsurface zones with ent lies between 230 and 390 m depth. IP surveys conducted abundant limonite or sulfide minerals commonly yields trace independently in the area show high resistivity diminishing element contents several orders of magnitude greater than and high chargeability increasing at depths consistent with an leached surface samples. Zones with elevated trace element inferred magmatic source (fig. 14). It is predicted, therefore, contents commonly are present within 10 meters of the exist-

7 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington ing erosion surface. Although tentative, certain geochemical Silver patterns have been recognized along with a distinct elemental suite. Anomalous trace elements present at the White River Silver is uniformly low in the White River area. The prospects and the patterns in which they are present are as highest Ag content in the Superior quarry hill area is 1.55 ppm follows: from a sample on the southwest flank of the hill near Washing- ton Highway 410. Here, elevated Ag is associated with high Bi and Sb contents. Gold Anomalous gold content, in excess of 100 ppb, was found Arsenic in outcrop by numerous samplers in the 1970s and 1980s. Most of these samples were in the Superior quarry and Quarry Elevated arsenic contents in excess of 300 ppm have Hill areas. High Au contents (500 to 1,800 ppb) do not tend to been found in samples collected from numerous locations in be present within silicified promontories. Rather, the highest the White River altered area. Enargite-bearing samples, areas concentrations have been found in the following settings: with high limonite content, and sulfide zones beneath the most 1. Soil samples from depressions surrounded by silicification. intensely leached capping tend to have the highest As contents. The best example is on the south face of Superior quarry Maximum values commonly exceed 1,000 ppm. Anomalous As hill area where a depression surrounded by vertical cliffs is commonly associated with anomalous amounts of Cu, where yielded soil samples with 1,600 ppb Au. Fill-in soil sam- enargite is likely the source mineral. However, some samples pling defined the area and later rock chip sampling and also contain low Cu contents and high As contents. Samples shallow air-track drilling produced similar values. with low Cu contents generally are present in oxidized rocks. 2. Advancement of the Superior quarry allowed sampling along a strike length of 200 meters in a highly fractured Copper zone trending N. 70° W. The fracture zone crosscuts silicification and did not crop out prior to mining. At Elevated copper contents are associated with the abun- each stage of mine advance, the gold contents increased, dant limonite and sulfide mineral-rich zones within the and Au contents in this structural zone are as much as strongly silicified areas. Concentrations in excess of 100 ppm 1,800 ppb. Associated with this zone are large pockets are common with maximum values greater than 12,000 ppm of white hydrothermal kaolinite and small amounts of (1.2 weight percent Cu) in an enargite-bearing sample from manganese oxide. the Superior quarry. The most anomalous Cu is in the Superior quarry hill area. 3. During excavation of overburden prior to mining near the west end of the Superior quarry, Ash Grove uncovered a circular depression about 30 m in diameter. The depres- Antimony sion had steep sides and a fracture pattern parallel to the steep faces, which dipped away in all directions. Excava- Antimony contents beneath leached capping in the most tion, which went to the current pit floor elevation, never siliceous core zones average about 25 ppm. Widespread intersected bedrock in the depression; however, abundant values greater than 50 ppm are common and maximum values highly limonitic material was present. Two samples are about 500 ppm. Most anomalous Sb is near the Superior containing 500 and 900 ppb Au were collected along quarry hill area, although areas of anomalous Sb also are pres- lower exposures within the depression. The depression ent south of White River (Sec. 10, T. 19 N., R. 8 E.), where also had highly anomalous concentrations of Te, Ba, Sb, several gossan samples have yielded high Sb contents. No Bi, Mo, As, Cu, Zn, and Ag. This depression may mark a drilling has been conducted in these areas. hydrothermal eruption crater. 4. Gold anomalies in soil samples suggest several linear Mercury trends as much as 400 m long and 15 m wide. Although Au anomalies are sometimes spatially associated with High mercury contents are present locally in silicified massive silicification, they are commonly adjacent to or rocks. Samples with greater than 500 ppb Hg are common and cross in and out of silicified rocks in softer zones with anomalies from 1,000 ppb to greater than 5,000 ppb are pres- abundant clay alteration that did not crop out prior to ent in the more intensely silicified and pyritized areas. mining. Observations in the Superior quarry hill area suggest that Bismuth, Tellurium and Selenium the gold anomalies are in softer fracture zones or in pipe-like structures cutting silicified rocks. These less resistant rocks Highly anomalous bismuth, tellurium and selenium typically were scoured out by glaciation and filled with glacial contents have been found in the Superior quarry hill area. The debris, which may make recognition by soil sampling difficult. most anomalous values for each element are about 200 ppm Anomalous Au contents are present in both sulfide mineral- Se, 200 ppm Te, and 900 ppm Bi. Higher Bi and Te contents bearing and oxidized, altered rocks. commonly are associated with high Sb contents.

8 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington Molybdenum In the southeast part of the quarry, bedded welded tuffs have been leached and altered to vuggy silica rock. The voids A strong molybdenum anomaly in drill holes and surface in the vuggy silica were developed from leaching of pumice samples is present south of the Scatter Creek quarry. The area, and phenocrysts and are larger than those developed in the bounded by Cady Hill, the east flank of Quarry Hill, and the altered andesite flow rock. Layering within the tuff indicates Scatter Creek quarry has yielded anomalous Mo contents in that bedding is subhorizontal. surface samples and in two drill holes. Molybdenum contents In the southwest part of the quarry, vuggy silica alteration in the drill holes commonly exceeded 100 ppm, and the high- is developed in a porphyritic intermediate composition rock est Mo content was 750 ppm. These anomalies are present (possibly dacite) and associated fragmental volcanic rocks. close to anomalous Pb and W (30–40 ppm) contents, but no Exposures of altered flow-folded dacite are present on the other strong elemental associations were noted. steep scarp just south of the quarry (fig. 7). The dacite shows The Mo anomalies may reflect a deep source for the relict flow banding and has textural layers that are interpreted hydrothermal alteration and mineralization exposed on the to be devitrification textures developed in glassy zones in the surface. The near-surface Mo anomaly is coincident with an IP dacite (fig. 23). Xenoliths as much as several cm in length are chargeability anomaly (fig. 14) and may be located over deep, present in the dacite. Vuggy silica alteration developed in the porphyry style copper-gold-molybdenum mineralized rock dacite and associated fragmental rocks contains larger voids (fig. 11). More work is needed to determine the significance of and is less massive and homogenous as compared to vuggy the anomalous molybdenum zone in this area. silica alteration developed in andesite flow rock. Other areas in the pit consist of massive, fine-grained silica that may repre- sent alteration of an aphyric glassy flow rock (fig. 24). Fine- Stop 1: Superior (Ash Grove) Quarry grained layering is commonly visible in rocks that have been silicified, and these rocks likely were bedded fine-grained tuffs The Superior (Ash Grove) silica quarry is located in and sedimentary rocks that are exposed in outcrops about 0.5 the southwest part of the White River acid-sulfate alteration km north of the quarry (fig. 6). system (figs. 8 and 18). The massive silica bodies consist Also in the steep face on the upper bench along the south- of vuggy silica that has been crosscut by several stages of west side of the pit, a narrow, north-northeast striking, felsite hydrothermal breccias and overprinted by chalcedonic veining porphyry dike cuts near horizontal flow foliated dacite. The and quartz veining and vug filling. The hydrothermal brec- dike cuts the center of the prominent hill and forms the point cias have been rebrecciated and subjected to continued acid of highest elevation (fig. 25). This dike extends across the pit leaching and vuggy silica development. Intense acid leaching to the northeast. The fine-grained dike rocks are buff-white to of host andesite and dacite flows and tuffs of the Fifes Peak tan in color and contain sparse 1-2 mm quartz phenocrysts. Formation by magmatic-hydrothermal fluids has resulted in Dike margins commonly exhibit faint flow banding accentu- the formation of vuggy silica rock with greater than 95 weight ated by weak limonite staining. The dike occasionally is cut by percent SiO2. Aluminum content is generally less than 0.5 irregular, hairline quartz veins. Near its margins, it contained weight percent (Al2O3), and Na, K, Mg and Ca oxides are all appreciable pyrite that is now oxidized. The dike, although less than 0.15 weight percent. Iron content as hematite and completely silicified, appears to postdate most massive hydro- more rarely as pyrite in the silica bodies is variable ranging thermal breccias in the Superior quarry; however, in the north- as high as 12 weight percent but more typically is less than 5 ern part of the pit, narrow hydrothermal breccia dikes cut and weight percent. Ti oxide content ranges from 0.6 to 1.6 weight contain fragments of the dike. This indicates the complex and percent. Mining for silica by the Ash Grove Cement Company multiphase nature of the breccias and associated hydrothermal is by open pit methods, and the silica is crushed and sized on activity. The presence of the felsite porphyry dike is significant site. The silica is used in the production of Portland cement. from several perspectives: Bordering the silica body exposed in the quarry are areas of • It is situated in the center of some of the most massive low relief and limited outcrops of advanced argillic alteration and well-developed hydrothermal breccias; consisting of kaolinite and alunite and locally pyrophyllite (fig. 18). • The dike is proximal to zones of abundant limonite and The rocks in the Superior quarry are highly altered and gossan that correspond to areas of pyritic hydrothermal it is commonly difficult to discern the original rock type (fig. sediments and associated hydrothermal vents; 19). Massive and homogenous gray vuggy silica in the central • and west part of the quarry contains voids where plagioclase The dike forms the core of a north-northeast-trending and pyroxene phenocrysts have been leached from andesite zone that contains some of the highest Au, As, Cu, and flow rock (fig. 20). Pyrite and enargite (figs. 21 and 22) are Bi contents; present most commonly in the hydrothermal breccias, and • The dike may be a late magmatic feature related to a also are present locally in the vuggy silica; however, at the dacite dome in the Superior quarry area (figs. 7 and 23). present mine level, the sulfide minerals are mostly oxidized and leached leaving numerous voids. Hematite is the primary Multiple stages of veining and hydrothermal brecciation oxidation product of the sulfides and gives the vuggy silica its core the vuggy silica zones and silicified rocks in the quarry. dark gray color. The earliest stage consists of hydrothermal breccia and veins

9 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington containing white chalcedonic silica (fig. 26). Locally large that have been recognized in the White River altered area. voids created during brecciation of the vuggy silica are filled Bedding in the tuff is about N. 10° E. 20° SE. To the south with white chalcedony that forms a massive white rock with across the road from the tuff breccia, hydrothermal breccia is little or no texture. Later stages of veining and hydrothermal well exposed (fig. 37). The matrix-supported breccia contains brecciation contain various colors of chalcedony ranging a heterogeneous mixture of subangular blocks as much as 50 from tan (fig. 27) to black depending on the amount of sulfide cm wide, including flow-banded lavas and (or) well bedded minerals present and extent of oxidation of the sulfide miner- tuffs, felsite, and porphyritic andesite. The blocks are silicified als. Veins of gray chalcedony cut vuggy silica rock and locally and include vuggy silica alteration. The breccia matrix con- develop a stockwork texture (fig. 28). Late stage hydrothermal sists of fine-grained silica and hematite. The hematite probably deposition of silica and sulfide minerals commonly show sedi- replaces sulfide minerals. mentary textures and horizontal banding indicating near-sur- face deposition of silica and sulfide minerals in hydrothermal vents (figs. 22 and 29). Stop 3: Scatter Creek (James Hardie) Silica Quarry In the southwest part of the quarry, a series of north-striking high-angle normal faults contain hematite-rich, clay-supported The Scatter Creek (James Hardie) silica quarry produces breccias and clay-filled fractures are present (figs. 30 and 31). high purity silica, greater than 97 weight percent SiO2, from Some clay zones are subhorizontal and likely reflect alteration leached and silicified volcanic rocks of the Fifes Peak Forma- of tuffs interbedded with the dacite flow (fig. 32). Gold contents tion and cross-cutting hydrothermal breccias (fig. 38). Alu- as much as 1.7 ppm are present in these fault and fracture zones. minum content of the silicified rock is generally less than 0.5

The clay minerals are montmorillonite ± dickite. Sedimentary weight percent (Al2O3), and Mg, Ca, Na, and K oxides are less structures, such as graded and cross bedding, in these open than 0.02 weight percent. Residual Ti oxide is present at as fractures indicate near-surface deposition and that the level of much as 0.8 weight percent and Fe oxide as hematite is vari- exposure of the hydrothermal system is relatively shallow. able but generally less than 0.5 weight percent. Silica is mined Detailed geochemical surveys of the silica bodies show by open pit methods and crushed and sized on site (fig. 39) for that anomalous concentrations of As, Au, Bi, Cu, Ga, Hg, Mo, shipment to James Hardie Building Products, Inc., for produc- Sb, Se, Te, and F are present locally. Elevated concentrations tion into fiber cement-based external siding and backer board known as Hardibacker. Silica is stockpiled on site and mining of F, as much as 0.75 weight percent, and TiO2, as much as 3.8 weight percent are present in the advanced argillic altera- is episodic, occurring when stockpiles are depleted. tion. Fine-grained rutile is present locally. In areas where Au Alteration in the Scatter Creek quarry consists of pervasive is anomalous, higher concentrations of Sn and W also are leaching of porphyritic andesite flows and pyroclastic rocks present. This geochemical suite is typical of that associated to form vuggy silica alteration (fig. 40). In the central part of with high-sulfidation gold deposits that are associated with the quarry, vuggy silica alteration is well developed in mas- porphyry Cu-Au systems (for example, Sillitoe, 2000). sive andesite flows and is characterized by voids from 2 to 4 mm in length formed from the leaching of plagioclase feldspar and pyroxene phenocrysts. The morphology of the leached Stop 2: Taugow phenocrysts is well preserved throughout most of the dark gray to black vuggy silica rock (fig. 41). Locally larger voids are Taugow, a hill midway between the Superior and Scatter present where leaching of clots of phenocrysts (glomeroporphy- Creek quarries, is named for the Taugow VABM marker near roclasts) has occurred. The large body of vuggy silica alteration the top of the hill (figs. 8 and 33). Rocks exposed on Taugow in the central part of the quarry trends E-W and has elevated include strongly altered tuff and tuff breccia cut by a narrow concentrations of Ag, As, Au, Cu, Hg, F, Mo, Se, Sb and Te. felsic dike and by hydrothermal breccias. Most pyroclastic rocks The highest concentration of Mo, as much as several hundred exposed are silicified or strongly altered alunitically. This brief ppm, is present in vuggy silica in the SE part of the quarry. stop will examine these hydrothermal features. In addition, if Molybdenum contents in excess of 700 ppm were encountered the weather is clear, this stop affords a 360° panorama of the in drill holes just south of the Scatter Creek quarry. In the White River altered area and Mount Rainier (see road log). north-central part of the quarry, a rib of vuggy silica alteration From the parking area (landing at end of road), the small about 1 meter wide was developed along a N.60–70°E. striking knob to the west consists of alunitically-altered tuff and tuff fault that localized the upward flow of acid magmatic-hydro- breccia containing relatively coarse-grained, pink-colored alu- thermal fluids (figs. 10 and 42). Bordering this vuggy silica nite (fig. 34). Alunite from here has been dated at 22.3±0.9 Ma is a zoned assemblage of advanced argillic alteration where by K–Ar methods (Weyerhaeuser Co., 1996), and a 40Ar/39Ar plagioclase and pyroxene phenocrysts have been replaced by date is in progress. alunite and kaolinite, grading outward into zones of illite and The north side of the road cut just before the end of the montmorillonite/chlorite (fig. 43). This zoning was developed as road exposes silicified, well-bedded tuff breccia (fig. 35) a result of buffering of the acid fluids by the country rock as it intruded by a narrow (2 to 3-cm-wide) fine-grained, quartz- moved outward from the fault (figs. 11 and 12). phyric felsic dike (fig. 36) and cut by hydrothermal breccias. Most pyrite and other sulfide minerals in the vuggy silica This dike and a similar dike mapped in outcrops on the lower alteration have been oxidized to a depth of greater than 125 southwest flank of Taugow are examples of only a few dikes m, and relict pods of sulfide minerals are only rarely present.

10 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Casts after pyrite are common, however, and indicate that as Osceola Mudflow and coeval phreatic and pumiceous mag- much as several weight percent pyrite was originally pres- matic tephras. The phreatic tephras, like the Osceola Mudflow, ent. Fine-grained specular hematite is the primary oxidation are clay-rich and contain hydrothermal minerals typical of product of pyrite and gives the vuggy silica its dark gray color. acid-sulfate systems. Mineralogy and stratigraphy demon- Within the upper few meters of the surface, hematite has been strate the genetic link between the Osceola Mudflow and its leached from the rock by surface weathering, and the resulting tephra and suggests how the hydrothermal system might have vuggy silica is white and distinctive from its generally black to influenced the eruption (Vallance and Scott, 1997; Vallance gray color (fig. 44). and others, 2003). Multiple stages of hydrothermal breccias and quartz and The Osceola Mudflow began as a water-saturated avalanche chalcedonic veins cut the vuggy silica rock in and outside the or a series of avalanches during phreatomagmatic eruptions at quarry. An early stage of hydrothermal breccias cemented by the summit of Mount Rainier. It filled valleys of the White River white chalcedony and cut by white chalcedony silica veins is system north and northeast of Mount Rainier to depths of 80 well developed in vuggy silica present in and outside the quarry to 150 m, flowed northward and westward more than 120 km, (fig. 45). On the periphery of the quarry, vuggy silica alteration covered more than 240 km2 of the Puget Sound lowland, covered has been hydrothermally fractured and locally more strongly another 160 km2 under the water of Puget Sound and extended brecciated and the resulting fractures and open spaces have been as much as 20 km under water (figs. 2 and 49). filled by white chalcedony. Hydrothermal fracturing and rota- Near Mount Rainier, deposits of the Osceola Mudflow tion of blocks of vuggy silica during hydrothermal brecciation cap ridges high above the Winthrop and Emmons Glaciers. locally developed large voids, as much as 0.5 m, that were filled Remnants also are present on top of Steamboat Prow and with dense white chalcedony that now form massive bodies of throughout the Inter Fork drainage basin. The homogene- white silica. A subsequent stage of hydrothermal breccias and ity of these deposits, the lack of hummocky terrain within veins containing tan (fig. 40) to dark gray chalcedony cut the 10 km of the summit, and the apparent fluidity suggest that early stage of white chalcedony veins. The later chalcedony the avalanches which initiated the Osceola Mudflow mixed veins and breccia contained fine-grained sulfides that have been thoroughly within 2 km of their source and abruptly began to oxidized to hematite (fig. 46), and the veins have elevated con- behave like an enormous water-saturated debris flow. centrations of As, Au, Cu, Hg, F, Mo, Sb, Se, and Te. Mapping the upper limits (inundation limit) of the High-angle normal faults and fractures cut the vuggy Osceola Mudflow along the steep-sided White River Valley silica alteration and are well exposed in the quarry. The most between Mount Rainier and Mud Mountain, 75 km down- prominent fault zone is 3 m wide, strikes N. 10-45° W. and stream, reveals that the peak-stage height of the mudflow dips 80° SW. It is filled with clay-supported fault breccia. attenuated sharply near the volcano then reached an equilib- Red clay-filled fractures, similar to Au–bearing fractures in rium height downstream. In the Inter Fork Valley, deposits of the Superior quarry, are present throughout the Scatter Creek the mudflow are present 400 m above the valley bottom. Five quarry. They consist of montmorillonite ± dickite and abun- kilometers downstream, the inundation limit is 200 m; farther dant hematite and are 1 to 12 cm wide (fig. 47). downstream, it stabilizes, varies between 85 m and 140 m, and An alteration zone of highly leached white rock consist- averages about 100 m. The decrease of the maximum inun- ing of cristobalite, opal, and kaolinite is present within a fault dation depth downstream by longitudinal spreading and by block in the central part of the quarry (fig. 48). This type of deposition was counteracted by the additional discharge from hydrothermal alteration is typical of alteration that forms in the West Fork 45 km downstream and by bulking of the flow the steam-heated environment above the paleo-ground water through the incorporation of eroded sediment. table. In this environment, H2S is oxidized by atmospheric Mud and debris of the Osceola Mudflow that ran up onto oxygen to form sulfuric acid that leaches alkalis and aluminum Goat Island Mountain, about 10 km from Mount Rainier, and from the rock leaving residual silica (for example, Schoen and onto a ridge dividing the White and Greenwater Rivers, about others, 1974; Hedenquist, 1990). Because the alteration forms 45 km downstream of Mount Rainier, allow the maximum in a near-surface, low temperature environment, the residual velocity and peak discharge of the flow to be estimated at silica is typically opal and cristobalite. The presence of steam- these two places (fig. 49). Clay-rich Osceola debris is present heated acid-leach alteration indicates that the level of exposure to an altitude of 2,054 m on Goat Island Mountain but not of the hydrothermal system in the Scatter Creek quarry is just up valley at an altitude of 1,944 m at the top of a low relatively shallow (fig. 11 and table 2). divide between and Fryingpan Creek. The debris on Goat Island Mountain suggests that the Osceola Mudflow ran up 110 m. Using v = (2gh)1/2, the velocity of the Part 2: The Osceola Mudflow in the flow must have been at least 46 m/s. Taking a typical nearby cross-sectional area in the Main Fork valley of about 190,000 Lower White River m2 suggests a discharge of approximately 8,000,000 m3/s. If the velocity was the same about 10 km downstream in General Features of the Osceola Mudflow the West Fork valley, a typical cross-sectional area of about 80,000 m2 suggests a discharge of approximately 4,000,000 About 5,600 years ago, an eruption of Mount Rainier m3/s there and a simultaneous discharge of about 12,000,000 triggered an edifice (sector) collapse that caused the 3.8–km3 m3. Similarly, at the confluence of the West and Main Forks

11 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington of the White River, mud and debris of the West Fork flow Hydrothermal Alteration in the Osceola Mudflow that ran up about 18 m onto a ridge dividing the White and Greenwater Rivers (fig. 49) allow a maximum velocity of 19 Preliminary study of the Osceola Mudflow and other m/s to be estimated. Taking a typical nearby cross-sectional Holocene debris flows from Mount Rainier indicates that area in the West Fork valley of at least 70,000 m2 suggests a three major types of hydrothermal alteration were present discharge of approximately 1,300,000 m3/s. If the simulta- on Mount Rainier prior to volcano collapse and formation of neous discharge along the Main Fork was as large, then the the debris flows (John and others, 2003)—(1) an intermedi- total discharge of the Osceola Mudflow near the confluence ate argillic assemblage consisting of smectite-group clay of the two forks of the White River would have been about minerals + pyrite ± silica ± barite ± anhydrite/gypsum; (2) 2,600,000 m3/s. advanced argillic alteration consisting of kaolinite + opal/ When it encountered a narrow gorge of the White River chalcedony + pyrite/marcasite ± alunite ± pyrophyllite; and at Mud Mountain that is only 300 m wide, the Osceola Mud- (3) jarositic alteration (jarosite + alunite + opal). Study of the flow spread out over glaciofluvial terraces of Vashon age that matrix of the Osceola Mudflow where unaffected by post- are as much as 110 m above the White River. As it continued flow surficial weathering indicates that it contains abundant westward, the mudflow poured over terrace scarps to form a fine-grained pyrite (fig. 50), in addition to the high clay con- spectacular pair of falls. The upper fall would have formed an tents previously documented by Crandell (1971) and Vallance arc more than 6 km wide and over 80 m high, and the second and Scott (1997). X–ray diffraction studies of the matrix of would have been more than 3 km wide and over 110 m high. the Osceola Mudflow also indicate the presence of fine- In the lowland, the Osceola Mudflow completely choked grained pyrophyllite and quartz. Alteration types 1 and 2 are the channel of the White River, which in pre-Osceola time common in the Osceola Mudflow and have been recognized followed the relatively confined valley of South Prairie Creek in exposures of the mudflow along the White River near southwestward to join the Puyallup River at Orting, then Greenwater (fig. 51). Alteration type 3 has not been found in flowed northwestward across the drift plain into the Green the Osceola Mudflow. River drainage (Crandell, 1963). When the White River Assemblage 1 alteration (smectite-pyrite) is present in reestablished normal flow, it flowed northwestward toward large numbers of clasts in the Osceola Mudflow and in other Auburn along the radically different course near the axis of Holocene debris flows from Mount Rainier (fig. 52). Clay the lahar lobe. minerals replace mafic phenocrysts and groundmass and fill The Osceola entered the Duwamish and Puyallup vesicles (fig. 53 and 54). Plagioclase phenocrysts commonly embayments of Puget Sound via deltas at the mouths of the are fresh or only weakly altered, mostly along microfractures. Green and Puyallup Rivers (fig. 49). Low gradients on the Preliminary x–ray diffraction and SEM–EDA studies suggest deltas caused the debris flow to pile as much as thicknesses of a range of smectite compositions. Pyrite is present as dissemi- more than 20 m near Auburn and Sumner (Dragovich and oth- nated crystals, lining vesicles, and filling narrow veins and ers, 1994). Deposits are generally present only in the subsur- microfractures. Pyrite abundance commonly reaches 5 to 10 face in the Duwamish and Puyallup Valleys. Wood-bearing, volume percent. Barite inclusions in vein-filling pyrite crystals clayey, gravel-rich deposits at depths of 20 to 100 m north- are present locally. west of Puyallup and north of Auburn show that the Osceola Assemblage 2 alteration (kaolinite-opal-pyrite ± alunite Mudflow retained its coherence and flowed more than 20 km ± pyrophyllite) is less abundant than assemblage 1 in debris under water. flows, probably because this alteration results in softer and Osceola Mudflow deposits comprise three facies. The more readily abraded rocks. It has been found in clasts in the axial facies forms normally graded deposits 1.5 to 25 m thick Osceola Mudflow as far as 50 km down valley from Mount in lowlands and valley bottoms and thinner ungraded deposits Rainier. This alteration is much more intense and pervasive in lowlands; the valley-side facies forms ungraded deposits than assemblage 1, resulting in complete replacement of igne- 0.3 to 2 m thick that drape valley slopes; and the hummocky ous minerals and groundmass (figs. 55 and 56). Some clasts facies, interpreted before as a separate (Greenwater) lahar, of this alteration in the Osceola Mudflow are hydrothermal(?) forms 2-to-10-m-thick deposits dotted with numerous hum- breccias that are cemented by opal, alunite, kaolinite, and mocks as much as 20 m high and 60 m in plan. pyrite. Alunite mostly forms fine-grained (<5 µm) lath-like The Osceola Mudflow transformed completely from crystals locally intergrown with kaolinite (fig. 57). Coarser- debris avalanche to clay-rich lahar within 2 km of its source grained alunite (as much as 30 µm long) locally fills vugs because of the presence of large volumes of pore water and (fig. 58). Pyrite and (or) marcasite content locally reaches 20 abundant weak hydrothermally altered rock within the pre- percent. Vug-filling anhydrite/gypsum, native sulfur, cinnabar, avalanche mass. A survey of clay-rich suggests that the barite, and fluorite are present locally (fig. 59). amount of hydrothermally altered rock in the pre-avalanche Most alunite crystals from Mount Rainier are Na-rich with mass determines whether a debris avalanche will transform molar K/(K+Na) ≈ 0.00 to 0.30. Compositional zoning is evident into a lahar or remain a largely unsaturated debris avalanche. in some well-formed crystals with cores generally having more The potential for transformation has important implications K–rich compositions than most of the outer parts of the crystals; for hazard assessments because lahars are more mobile than some crystals also have very narrow (<1 µm) K–rich rims. Some debris avalanches, and therefore spread more widely and travel alunites contain P–rich domains with as much as several weight

much greater distances down valley. percent P2O5 (fig. 58). We have not detected phosphate minerals,

12 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

such as woodhouseite (CaAl3(PO4)SO4(OH)6) or crandallite of the clay matrix are dark gray due to the presence of abun-

(CaAl3(PO4)2(OH)5•H2O), in our samples, although Zimbel- dant fine-grained pyrite (fig. 50) man (1996) reported them from outcrops near the summit. Chemical analyses of 10 samples of altered rocks from the Osceola Mudflow (mostly pyrite-rich smectite alteration) Stop 5: Osceola Mudflow in the Corliss Gravel and nine lahar matrix samples indicate strong enrichment of Quarry, Enumclaw, Washington sulfur, but little or no enrichment in most elements character- istic of base- or precious-metal mineral deposits (Au, Ag, As, The Corliss quarry produces sand from fluvial gravels Sb, Hg, Tl, Cu, Pb, Zn, Bi). Previous geochemical studies of and glacial kame terraces that banked along the west side of altered rocks by Zimbelman (1996) and Bruce (1998) showed the Cascades Range during late Pleistocene continental glacia- similar results, although most of their samples were oxidized tion that covered the Puget Sound lowlands. The Osceola surface samples. Mudflow is exposed locally in the quarry as a 4- to 5-m–thick deposit overlying the fluvial-glacial deposits (fig. 61). In this stop, we will compare characteristics of the Osceola exposed Stop 4: Osceola Mudflow along White River here to the Osceola exposed near Greenwater (stop 4), about near Greenwater, Washington 25 km farther up the White River Valley and closer to the source of the mudflow on Mount Rainier. Many features of the Osceola Mudflow, a clay-rich lahar The Osceola Mudflow in the Corliss quarry consists mostly derived from edifice collapse of Mount Rainier’s hydrother- of rounded cobbles and small boulders as much as about 50 cm mal system 5,600 calendar years B.P. (4,800 14C years B.P.), wide (fig. 62). Quaternary andesites from Mount Rainier are the are exposed in outcrops along the right (northeast) bank of most common clasts, but clasts of Tertiary andesites, welded the White River near Greenwater. Note that, whereas axial- tuffs and granites also are common. The ratio of rocks from facies deposits like this one range from a few to 20 m thick, Quaternary Mount Rainier to older rocks is much lower here the Osceola Mudflow filled the valley in this area to the much than at the Greenwater locality, an indication of “bulking” of greater depth of 100 m. the mudflow by incorporation of surface materials that it passes Erosion by the White River has exposed 8 m of Osceola over. Hydrothermally-altered clasts are much less common than Mudflow deposit at this location (fig. 51). Underlying the at Greenwater, probably indicating both dilution by incorpora- Osceola are runout facies of clay-poor lahars derived from an tion of surface materials (bulking) and mechanical abrasion of eruptive episode of Mount Rainier dated between 6,800 and the softer, hydrothermally-altered rocks during transport. The 7,200 calendar years B.P. (6,000 to 6,400 14C years B.P.). Osceola here also contains small trees and tree branches that The exposure here provides excellent views of the were incorporated during flowage (figs. 61 and 62). sedimentologic characteristics of a clay-rich lahar deposit. The matrix of the Osceola Mudflow in the Corliss quarry The outcrop is normally graded, not only with respect to the is a gray sand that is noticeably more clay rich than the coarse gravel-size fraction, but also with respect to the frac- underlying fluvial and glacial deposits, but much less clay rich tion of sand within the matrix (sand versus sand + silt + clay). than the matrix of the Osceola at the Greenwater stop. A 1 to 2 Conversely, clay (chiefly of hydrothermal origin in the pre- cm thick, Fe-rich hardpan is present locally at the base of the collapse edifice) and other particles affected by hydrothermal Osceola (fig. 63). alteration increase up-section within the outcrop. Deposits show a progressive downstream improvement in sorting, increase in sand and gravel, and decrease in clay. References These downstream progressions are caused by incorporation (bulking) of well-sorted gravel and sand. Normally graded axial deposits, like those in this outcrop show similar trends Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, from top to bottom because of bulking. The coarse-grained J.B., 1965, Late Pleistocene stratigraphy and chronology in basal deposits in valley bottoms are similar to deposits near southwestern British Columbia and northwestern Washing- inundation limits. Normal grading in deposits is best explained ton: Geological Society of America Bulletin, v. 76, no. 3, p. by incremental aggradation of a flow wave, coarser grained at 321-330. its front than at its tail (fig. 60). Arribas, Antonio, Jr., 1995, Characteristics of high-sulfidation A wide variety of hydrothermally altered rocks and epithermal deposits, and their relation to magmatic fluid, in hydrothermal minerals from Mount Rainier are present as Thompson, J.F.H., ed., Magmas, fluids, and ore deposits: clasts and matrix in the mudflow here. The larger clasts, as Mineralogical Association of Canada Short Course Series, much as 1 m in wide, are mostly fresh or weakly altered to v. 23, p. 419-454. a smectite-pyrite assemblage. More strongly altered clasts, notably advanced argillic assemblages (kaolinite-pyrite- Ashley, R.P., Rytuba, J.J., John, D.A., Blakely, R.J., Box, S.E., opal±alunite), tend to form much smaller, well-rounded clasts. and Newport, G., 2003, The White River silica deposits, Much of the mudflow matrix here is clay rich. The clay size Washington: Upper parts of an early Miocene porphyry Cu- fraction of the matrix contains smectite, kaolinite, alunite, Au system? [abs.]: Geological Society of America Abstracts hydrothermal quartz, and minor pyrophyllite. Unoxidized parts with Programs, v. 35, n. 6, p. 232-233.

13 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Blakely, R.J., 1995, Potential theory in gravity and magnetic Hedenquist, J.W., Arribas, Antonio, Jr., and Gonzalez-Urien, applications: New York, Cambridge University Press, 441 p. Eliseo, 2000, Exploration for epithermal gold deposits, in Hagemann, S.G., and Brown, P.E., eds., Gold in 2000: Blakely, R.J., and Simpson, R.W., 1986, Approximating edges Reviews in Economic Geology, v. 13, p. 245-277. of source bodies from magnetic or gravity anomalies: Geo- physics, v. 51, p. 1494-1498. Huntting, M.T., 1955, Gold in Washington: Washington Divi- sion of Mines and Geology, Bulletin 42, 158 p. Blakely, R.J., Wells, R.E., and Weaver, C.S., 1999, Puget Sound aeromagnetic maps and data: U.S. Geological Survey John, D.A., Breit, G.N., Rye, R.O., Sisson, T.W., and Vallance, Open-File Report 99–514, http://geopubs.wr.usgs.gov/open- J.W., 2003, Hypogene hydrothermal alteration of Quater- file/of99-514. nary volcanic rocks from Mount Rainier, Washington [abs.]: Geological Society of America Abstracts with Programs, v. Breit, G.N., Rye, R.O., John, D.A., Kester, C.L., and Berry, 35, n. 6, p. 553. C.J., 2003, Isotopic studies of sulfur-bearing minerals in the clasts and matrix of Holocene debris flows from Mount Kelly, H.J., Strandberg, K.G., and Mueller, J.I., 1956, Ceramic Rainier, Washington [abs.]: Geological Society of America industry development and raw-material resources of Abstracts with Programs, v. 35, n. 6, p. 553. Oregon, Washington, Idaho, and Montana: U.S. Bureau of Mines Information Circular 7752, 77 p. Bruce, V.L., 1998, Geochemistry of hydrothermal alteration along a radial transect from the summit of Mount Rainier, Livingston, V.E., Jr., 1971, Geology and mineral resources of Washington: Riverside, University of California, M.S. King County, Washington: Washington State Division of thesis, 120 p. Mines and Geology Bulletin, n. 63, 200 p. Callaghan, Eugene, 1940, Alunite deposits near Enumclaw, Mattinson, J.M., 1977, Emplacement history of the Tatoosh King and Pierce Counties, Washington: unpub. U.S. Geo- volcanic-plutonic complex, Washington; ages of zircons: logical Survey report, 12 p. plus table. Geological Society of America Bulletin, v. 88, p. 1509- 1514. Christiansen, R.L., and Yeats, R.S., 1992, Post-Laramide geology of the U.S. Cordilleran region, in Burchfiel, B.C., McCulla, M.S., 1986, Geology and metallization of the White Lipman, P.W., and Zoback, M.L., eds., The Cordilleran River area, King and Pierce Counties, Washington: Corval- Orogen; Conterminous U.S.: Boulder, CO, Geological lis, Oregon State University, Ph.D. dissertation, 213 p. Society of America, the Geology of North America, v. G-3, p. 261-406. Mullineaux, D. R., 1974, Pumice and other pyroclastic deposits in Mount Rainier National Park, Washington: U.S. Crandell, D.R., 1963, Surficial geology and geomorphology Geological Survey Bulletin 1326, 83 p. of the Lake Tapps quadrangle, Washington: U.S. Geological Survey Professional Paper 388-A, 84 p. Plumlee, G.S., Rye, R.O., Breit, G.N., and John, D.A., 2003, Chemical modeling of volcanic gas interactions with Crandell, D.R., 1971, Postglacial lahars from Mount Rainier ground water and andesite: Insights into hydrothermal National Park, Washington: U.S. Geological Survey Profes- alteration at Mount Rainier, Washington [abs.]: Geological sional Paper 677, 75 p. Society of America Abstracts with Programs, v. 35, n. 6., p. 553. Dragovich, J., Pringle, P.T., and Walsh, T.J., 1994, Extent and geometry of the mid-Holocene Osceola Mudflow in the Ransome, F.L., 1909, The geology and ore deposits of Gold- Puget Sound Lowland—Implications for Holocene sedi- field, Nevada: U.S. Geological Survey Professional Paper mentation and paleogeography: Washington Geology, v. 22, 66, 258 p. no. 3, p. 3–26. Rye, R.O., Bethke, P.M., and Wasserman, M.D., 1992, The Glover, S.L., 1936, Nonmetallic mineral resources of Wash- stable isotope geochemistry of acid-sulfate alteration: Eco- ington: Washington Division of Geology Bulletin 33, 135 p. nomic Geology, v. 87, p. 225-262. Gustafson, L.B., and Hunt, J.P., 1975, The porphyry copper Rytuba, J.J., John, D.A., Foster, Andrea,, Ludington, S.D., and deposit at El Salvador, Chile: Economic Geology, v. 70, p. Kotylar, Boris, in press, Hydrothermal enrichment of gal- 857-912. lium in zones of advanced argillic alteration; examples from the Paradise Peak and McDermitt ore deposits, Nevada, in Heald, P., Foley, N.K., and Hayba, D.O., 1987, Comparative Bliss, J.D., Moyle, P.R., and Long, K.R., eds., Contributions anatomy of volcanic-hosted epithermal deposits: Acid sulfate to Industrial-Minerals Research: U.S. Geological Survey and adularia-sericite types: Economic Geology, v. 82, p. 1-26. Bulletin 2209, Chapter C, 34 p. Hedenquist, J.W., 1990, The thermal and geochemical signa- Schoen, R., White, D.E., and Hemley, J.J., 1974, Argillization ture structure of the Broadlands-Ohaaki geothermal system: by descending acid at Steamboat Springs, Nevada: Clays Geothermics, v. 19, p. 151-185. and Clay Minerals, v. 22, p. 1-22.

14 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Sillitoe, R.H., 1999, Styles of high-sulphidation gold, silver, Valentine, G. M., 1960, Inventory of Washington minerals-Part and copper mineralization in the porphyry and epithermal I, Nonmetallic minerals, 2nd ed., revised by M.T. Huntting: environments: PacRim ’99, Bali, Indonesia, 10-13 October, Washington Division of Mines and Geology Bulletin 37, v. Proceedings, p. 29-44. 1, 175 p. Sillitoe, R.H., 2000, Gold-rich porphyry deposits: Descrip- Vallance, J.W., and Scott, K.M., 1997, The Osceola Mudflow tive and genetic models and their role in exploration and from Mount Rainier: Sedimentology and hazard implica- discovery, in Hagemann, S.G., and Brown, P.E., eds., Gold tions of a huge clay-rich debris flow: Geological Society of in 2000: Reviews in Economic Geology, v. 13, p. 315-345. America Bulletin, v. 109, p. 143-163. Sisson, T.W., Lanphere, M.A., and Calvert, A.T., 2003, Altera- Vallance, J.W., Breit, G.N., and John, D.A., 2003, Involvement tion and the magmatic history of Mt. Rainier, Washington of a hydrothermal system in the catastrophic 5600 BP erup- [abs.]: Geological Society of America Abstracts with Pro- tion of Mount Rainier [abs.]: Geological Society of America grams, v. 35, n. 6, p. 552. Abstracts with Programs, v. 35, n. 6, p. 552-553. Sisson, T.W., Vallance, J.W., and Pringle, P.P., 2001, Prog- Weyerhaeuser Company, 1996, Summary Report, Weyer- ress made in understanding Mount Rainier’s hazards: Eos haeuser Exploration Package, White River Properties, King (Transactions, American Geophysical Union), v. 82, p.113- County, Washington, unpublished internal report, 50 p. 120. Zimbelman, D.R., 1996, Hydrothermal alteration and its influ- Steven, T.A., and Ratte, J.C., 1960, Geology of ore deposits ence on volcanic hazards—Mount Rainier, Washington, a of the Summitville district, San Juan Mountains, Colorado: case history: Boulder, University of Colorado, Ph.D. dis- U.S. Geological Survey Professional Paper 343, 70 p. sertation, 384 p. Stoffregen, R.E., 1987, Genesis of acid-sulfate alteration and Zotov, Alexandre, Mukhamet-Galeev, Alexandre, and Schott, Au-Cu-Ag mineralization at Summitville, Colorado: Eco- Jacques, 1998, An experimental study of kaolinite and nomic Geology, v. 82, p. 1575-1591. dickite relative stability at 150-300°C and the thermody- namic properties of dickite: American Mineralogist, v. 83, Tabor, R.W., Frizzell, V.A., Jr., Booth, D.B., and Waitt, R.B., p. 515-524. 2000, Geologic map of the Snoqualmie Pass 30 x 60 minute quadrangle, Washington: U.S. Geological Survey Geologic Investigations Series Map I-2538, scale 1:100,000.

15 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

127°W 126° 125° 124° 123° 122° 121° 120° 119° 118° 117°

49°N CANADA

Mount Baker UNITED STATES

er

v

i R

Glacier Peak

mbia

Colu 48°

Seattle

IDAHO WA

SH.

47° White Mount Rainier River Goat Rocks volcano Mount St. Helens Mount Adams WASH. 46° River OREG Columbia Portland Quaternary High Cascades volcanic rocks Mount Hood Late Eocene to Pliocene 45° Mount Western Cascades arc rocks Jefferson Late Eocene to middle Three Miocene granitic rocks Western Sisters Major Quaternary volcanoes 44° Cascades Major faults Newberry caldera Deposit Types High Porphyry Cu 43° Cascades Cu breccia pipe Polymetallic vein X Crater Lake Silica-alunite Simple Sb Low-sulfidation epithermal Au-Ag ORE. 42° Hot-spring Hg CALIF. Silica-carbonateNEVADA Hg Volcanogenic U Medicine Lake acific Ocean Epithermal Mn Mount Shasta

41° P NEVADA CALIF.

Lassen Peak

40°

0500KILOMETERS

Figure 1. Map showing location of the Western Cascades and High Cascades arcs and mineral deposits in the northwestern United States. Also shown is location of the White River altered area. Mineral deposits from U.S. Geological Survey Mineral Resources Data System database.

16 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Seattle ? 25 km Kent Tacoma

et Enumclaw Pug Puyallup Sound Buckley Orting Electron Mount Rainier

OSCEOLA ELECTRON/ COLLAPSE ROUND PASS COLLAPSES PARADISE COLLAPSE

Figure 2. Map showing areas inundated by Holocene debris flows from Mount Rainier. The Osceola and Electron Mudflows and the Para- dise and Round Pass lahars all have clay-rich matrixes and contain abundant clasts of hydro- thermally altered rocks. Modified from Sisson and others (2001).

Figure 3. Photograph of vuggy silica alteration in the Scatter Creek (James Hardie) silica quarry, White River altered area. -covered Mount Rainier is in the back- ground.

17 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington 30' ° 122 ILOMETERS 0K ILES 5M ETERS VAL 50 M 4 CONTOUR INTER 0 01 45' ° 122 3 2 1 1 6 3 1 1 1 1 5 Geologic map of the SW quarter Snoqualmie Pass 30 x 60

00'W ° 123 15'N 00' ° ° 47 47 Figure 4. minute quadrangle, showing field trip stops. Geology from Tabor and others minute quadrangle, showing field trip stops. Geology from Tabor (2000). Red box shows White River altered area and outline of figure 8.

18 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington LIST OF MAP UNITS Rhyolite unit of Clear West Peak Man-Modified land (Holocene) Intracaldera rhyolite Alluvium (Holocene and Pleistocene) Extracaldera rhyolite tuff Bog deposits (Holocene and Pleistocene) Rhyodacite tuff Landslide deposits (Holocene and Pleistocene) Sun Top unit Mass-wastage deposits (Holocene and Pleistocene) Chenuis Ridge unit Talus deposits (Holocene and Pleistocene) Volcanic rocks of Eagle Gorge (Miocene and Oligocene) Lahar deposits (Holocene and Pleistocene) Ohanapecosh Formation (Oligocene)

Tuff member of Lake Keechelus Surficial deposits, undivided (Holocene and Pleistocene) Volcanic rocks (Oligocene) Alpine glacial deposits (Pleistocene)

Deposits of Vashon stade of Fraser glaciation of Armstrong and others (1965) of Cordilleran ice sheet (Pleistocene) Diabase, gabbro, and basalt (Oligocene? and Eocene) Recessional outwash deposits

Ice-contact deposits Contact

Till High-angle Fault

Advance outwash deposits Major Folds Vashon Drift, undivided Anticline Glacial and nonglacial deposits of pre-Fraser glaciation age (Pleistocene) Syncline Alpine glacial drift of pre-Fraser glaciation age (Pleistocene) Overturned Syncline

Strike and dip of bedding 20 Andesite of Mount Rainier (Pleistocene) Inclined

20 Basalt of Canyon Creek (Pleistocene) Inclined, top known

30 Basaltic tuff and breccia Overturned

30 Basalt of Dalles Ridge (Pliocene) Overturned, top known

Howson Andesite (Miocene) Vertical

Volcaniclastic rocks of Cooper Pass (Miocene) Vertical, top towards ball

Horizontal Carbon River stock (Miocene) Strike and dip of foliation 20 Intrusive rocks (Miocene and Oligocene) Inclined Pyroxene andesite porphyry Vertical Tonalite 40 Lineation Altered porphyry Zone of sheared rock Dacite porphyry Zone of silicified rhyolite Fifes Peak Formation (Miocene) Crest of moraine Volcaniclastic rocks Spillway Andesite and basalt megabreccia

Crystal-lithic tuff Landslide arrow 5 Field trip stops

Figure 4. Geologic map of the SW quarter of the Snoqualmie Pass 30 x 60 minute quadrangle, showing field trip stops. Geology from Tabor and others (2000). Red box shows White River altered area and outline of figure 8—Continued.

19 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 5. Heterolithic breccia (lahar) in the Fifes Peak Formation. Rock consists of unaltered clasts of several types of andesite in a propyliti- cally or argillically altered matrix.

Figure 6. Subhorizontal, finely bedded tuffs from small outcrop about 0.5 km north of the Superior quarry. Tuff is variably silicified or altered to alunite.

Figure 7. Silicified flow-banded dacite showing large flow fold open to the left side of photo. Cliffs above WA SR 410 south of the Superior quarry.

20 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington 47' ° Qa 121 Qls Tfpa alunite Bridge Camp Tfpr Tfpa 48' ° 121 Qls Silicification and alunite Pervasive argillic alteration Mapped Alteration tions of silica quarries and other geographic Qvl Z, zunyite locality. Geologic map modified from Tabor Geologic map modified from Tabor Z, zunyite locality. Qls 49' Tfpa ° Qad Dickite 121 ± k Formation rhyolite; Tfpa, Fifes Peak andesite. Tfpr quarry Z Montmorillinite Halloysite Montmorillinite Scatter Creek Qa Cady Hill 50' ° 121 ugow Ta Hill Pyrophyllite Illite Kaolinite Quarry Tfpr Tfpa 51' ° Alteration Types (PIMA)—see table 1 121 Qg Qa Silica Alunite Dickite quarry Superior Tfpa quarry Qg Denny-Renton Qg 52' ° 121 Qg Qa Tfpa Qvl 53'W ° Contact Fault, dotted where concealed IP survey (fig. 14) 121 500 Tfpa Tfpa 1,000 0 1,000 meters Map showing distribution of hydrothermal alteration, Portable Infrared Mineral Analyzer (PIMA) alteration mineralogy, and loca Map showing distribution of hydrothermal alteration, Portable Infrared Mineral Analyzer (PIMA) alteration mineralogy,

10' 09' ° ° 11'N ° 47 47 47 Figure 8. features in the White River area. Areas of hydrothermal alteration modified from unpublished mapping by Weyerhauser Co. (1996). features in the White River area. Areas of hydrothermal alteration modified from unpublished mapping by Weyerhauser and others (2000). Qa, alluvium; Qls, landslide deposits; Qvl, lahar deposits; Qg, glacial deposits, undivided; Tfpr, Fifes Pea and others (2000). Qa, alluvium; Qls, landslide deposits; Qvl, lahar Qg, glacial deposits, undivided; Tfpr,

21 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 9. Voids developed from leaching of plagioclase and pyroxene phenocrysts in a porphyritic andesite flow in the Fifes Peak Formation by acidic hydrothermal fluids during vuggy silica alteration. Late, white chalcedonic silica locally replaces and infills the gray vuggy silica. Scatter Creek quarry.

Figure 10. Sharp contact shown by pen between vuggy silica alteration (VS) and alunitic alteration (AA) exposed in narrow northeast-trending rib in the Scatter Creek quarry (also see figs. 38 and 42).

22 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Schematic reconstruction of a high-sulfidation deposit

Steam-heated acid-leached zone Disseminated Au-Ag in vuggy quartz X X X X X XXXX White River V V V V V V X XX X X V V V V V Illite out to V V X XXXDome X V V V V V illite/smectite X XXV X Ignimbrite XXX Quartz-dickite/kaolinite X Quartz-alunite

Au-enargite/luzonite in vuggy quartz 500m Au-tennantite in vuggy quartz 500m

(modified from Sillitoe, 1999) Barren Intermediate argillic alteration (sericite up to pyrophyllite) Porphyry stock + + + Chalcopyrite in K-silicate alteration +

Figure 11. Schematic model for high-sulfidation gold deposits, showing zoning of hydrothermal alteration assemblages and ore types. Most of the White River altered area is inferred to have formed in the uppermost part of this type of hydrothermal system where vuggy silica altera- tion is extensively developed in permeable horizons (green box). Figure courtesy of Antonio Arribas, Jr., and based on Sillitoe (1999). -30 250°C - +Quartz HSO4 ALUNITE KAOLINITE KAOLINITE MUSCOVITE -32 K-FELDSPAR

- (Na,K)SO4 2 O

ƒ PYRITE HEMATITE -34 COVELLITE DIGENITE CHLORITE LOG H2S

PYRITE+BORNITE -36 CHALCOPYRITE

ENARGITE TENNANTITE HS- -38 2 4 6 8 pH

Figure 12. Log ƒO2-pH diagram at 250°C, total sulfur=0.02 molal, salinity=1 molal with Na/K=9, and quartz saturation, modified from Heald and others (1987). Magmatic-hydrothermal fluids forming vuggy silica alteration (star) likely had pH<2 where Al solubility dramatically increases (Stoffregen, 1987). Progressive reaction of this acidic fluid with relatively reduced, plagioclase feldspar-rich wall rocks increased the pH and lowered the oxygen fugacity of the fluid result- ing in zones of quartz-alunite, quartz-kaolinite, and quartz-muscovite (illite) alteration outward from fluid conduits as indicated by arrow. At higher temperatures (>270°C), pyrophyllite will replace kaolinite. Stability relations between kaolinite and dickite are uncertain and may reflect higher temperature stability of dickite and/or kinetics (Zotov and others, 1998).

23 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

122o 121o50' 121o40' A

Magnetization boundaries

47o15'

B A

White River Fault Zone

47o05'

B Qa Alluvium (Holocene and Pleistocene) Ql Landslide deposits (Holocene and Pleistocene) Qlh Lahar deposits (Holocene and Pleistocene)

Qag Alpine glacial deposits (Pleistocene) Qvr Recessional outwash deposits Qvi Ice-contact deposits Qvu Vashon Drift, undivided o 47 15' 5' Qpfa Alpine glacial drift (Pleistocene)

Qcc Basalt of Canyon Creek (Pleistocene)

Tf Fifes Peak Formation (Miocene) White River fa Tfci Intracaldera rhyolite Tfce Extracaldera rhyolite tuff ultzone Tfrt Rhyodacite tuff Tfst Sun Top unit Tfcr Chenuis Ridge unit

Teg Volcanic rocks of Eagle Gorge (Miocene and Oligocene)

To Ohanapecosh Formation (Oligocene) Diabase, gabbro, and basalt 47o05' Tdg (Oligocene? and Eocene)

Tp Puget Group

Zone of silicified Rhyolite 0246810KILOMETERS

Magnetic anomaly low

Figure 13. A, Aeromagnetic anomalies of the White River altered area and surrounding regions. White dots represent magnetic contacts calculated automatically using the method of Blakely and Simpson (1986). Magenta stars indicate location of Superior (Ash Grove) and Scatter Creek (James Hardie) quar- ries. Labels A and B indicate negative and positive anomalies discussed in text. B, Geologic map of the White River altered area, modified from Tabor and others (2000). The bold, dotted polygon shows the location of the aeromagnetic low, determined from the magnetic-contact analysis. Red line shows induced polarization (IP) profile shown in figure 14.

24 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington ity anomalies represent near-surface ity anomalies represent near-surface . B 16 Inversion modeling completed by Gradient Geophysics, Inc., using University of British Columbia program, DCIP2D. High resistiv

Figure 14. silicification and high chargeability anomalies indicate the presence of sulfide minerals. Profile line shown on figures 8

25 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

122o 121o50' 121o40' A

47o15'

B A

47o05'

B

47o15'

Gravity station

Magnetic anomaly low

47o05'

0246810KILOMETERS

Figure 15. A, Observed aeromagnetic anomalies transformed to pseudograv- ity. B, Observed isostatic residual gravity anomalies. Yellow triangles are gravity stations. See figure 13 for other symbols.

26 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

-121°55' -121°50'

A

"

0

3

'

2

1

° 7 4 X Magnetic Susceptibility (SIU X 1000) >1 B 0.5-1 0.2 - 0.5 A 0.1-0.2 0.05 - 0.1 < 0.05

" IP line A (fig. 14)

0

3

'

7

°

7 4

B "

0 nT

3

'

2 1

° 259.1 7

4 179.7 128.1 92.6 60.8 33.6 6.9 -17.3 -42.4 -64.4 -84.3 -103.4 -129.2

-163.7 "

0 -212.6

3

'

7

°

7 4

2500 0 2500 5000 Meters

Figure 16. Ground-magnetic studies. A, Map showing the location of all susceptibility measurements (dots) with respect to aeromagnetic anomalies. Susceptibility color coded by value. Stipple pattern, is zone of silici- fied rhyolite (Tabor and others, 2000). Labels A and B indicate anomalies discussed in text. X indicates sus- ceptibility measurement of laterally restricted area of unaltered basalt. B, Representative ground-magnetic profile plotted along route and in map projection. Black and white fill indicates positive and negative anomaly, respectively, relative to base station at Taugow.

27 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington Profile 6-5-4

1000.00 500-point filter Individual Measurements 500.00

0.00

-500.00

1000.00 Relative Magnetic Intensity, nT -122.94 -122.92 -122.90 -122.88 -122.86 -122.84 -122.82 -122.80 -122.78

Figure 17. Ground-magnetic profile across White River altered zone. See figure 16 for profile location. Values along profile have been projected onto an east-west line and are shown relative to base-station measurements at Taugow. Green dots are individual measure- ments; red line is low-pass version of individual measurements. Arrow indicates magnetic gradient discussed in text.

Figure 18. View of the Superior (Ash Grove) quarry from Taugow.

28

Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

0 0

2

6

6

1 5 1

500 250 000 750 500

0

0 0

6 1

155 0

N668 N668 N668 N667 N667

50

1

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8 4 5

1 0

15 57 1 N

1530 TREES

0

9

4 1

0

156

0

0

1

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5

1 1 TREES TREES

1550

300'

3750 E130 1540

70

15

0

5

5 1

Ash Grove Superior Quarry (8.5 x11).dwg [Ash Grove Superior Quarry (8.5 x11).mcl] 10/10/2003

0

6

5 1

Scale in Feet

550

1 60

BRUSH

15 0

0 8

9 100' 200'

4 0 TREES

4 0 1

1 (G. Heinemeyer, 2003)

150

156

0

1 5

BRUSH

1

0

3

5

1550 1 1520

0

3

5

1

3500 E130 ASHGROVE - SUPERIOR QUARRY

0 4 GENERALIZED GEOLOGY 15

1570

0 8

050'

5 1

0 BRUSH 5 TREES

15

0

6

5 1 0

154

50 15 0 155

0 0 8

56 5

1 0 1 5

5 1560 1 70 5 1

1570

3250 E130

0

5

5

1 0

6

5 0

0 1

6

7 0 0

5

5 7 0 5

1

0 1 5 5

1 1

46 145

1 0

8

4 BRUSH 1

0

2 1500

5

40 1

5 BRUSH 1

0 0

8

5 1 0

1

7 6 5

1 1 1560

0

156

0

5 15

1590

0

0

8 5

156 70

1

0 0

5

15

5 56

--complex, multi-staged breccias of a 1 0 1 5 5 1 60 15

TREES

3000 E130 --local dacitic flow dome centered in the Ashgrove Hill area.

BRUSH

0 9 0

7 15 5

1

0

5

5 0

1

0

7

3

5

5 1 with a rock flour matrix. Various breccia stages often crosscut one another. widely varying textures and sub-horizontalwestern flow portion layering. of the Flow Superior dome Quarry rocks display in numerous the flattened pumice fragments and welded eutaxitic textures. In the northwesternflow portion foliation. of the The dacite flow dome is host to the extensive hydrothermal breccia Superior Quarry, flow dome rocks consist of tuffs with only rare indications of hydrothermal origin. Breccias varyintrusions from to massive, fine coarse grain heterolithologic "shatter" brecciation consisting of host rock fragments ignimbrites, and possible local accumulations of vent facies pyroclastics with masses in the Superior quarry. Hydrothermal Breccia Masses Breccia massed commonly attenuate into narrow breccia dikes and veins. Dacite Flow Dome

Flow dome rocks consist of nearly horizontal, composite layers of flows, tuffs,

1

0 0 6

45 0 1 6 15 0 0

4 0 0 1

1 480 4 5 0 5 1

1 2 1 15

5 0

1 9

4

1

?

2750 E130

0

5

0

5

7

1

5

1

0

58 1

0

7

5 0

1 9

5

0 1

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1

0

1550 2

0 6

1 1

0 ?

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6

1 0 ? 158

0

8

? 0 5

1

0

0

6 155

7

1560 5

5

1

1 --hydrothermally derived,

0 4

5 0 70 0 5 1 8 1 2 4 0

1 6 15

1500 4

1

0

8 ?

5 ?

? 1

?

? 2500 E130

0

0

6

1 0 9 5

1

1500 480

0 1

1

5 0 1450 0

1 9 7

5 5

1

1

1530 1550

80 15 ?

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0

16 --trending north-south across Ashgrove Hill. ? ? 0 TREES 8 5

1

0

4

0 6

610 630

1 1

0 1 1

9 6

0 5 1

1

57

1

1590 1550 0

0

6 0

1 2 6

1 1630 Generalized geologic map of the Superior quarry.

0 faint flow banding accentuated by limonite staining. The felsite is cut one location, a late hydrothermal breccia dike cuts the dike.

are commingled with the fine volcanic ash. cuts most of the hydrothermal breccia events. Dike margins exhibit a "pool accumulates" consisting of dark gray to black, horizontally by irregular, milky quartz veins and fine hairline veinlets. In at least 8 bedded, fine grained, volcanic ashpumice. containing fragments High of volumes ash (+7 and vol. percent) of bedded sulfides (pyrite) Buff-white to tan, fine-grained dike with occasional quartz phenocrysts Felsite Porphyry Dike Bedded, Vent Facies Micro-Pyroclastics

5

1 2250 E130 Lithology BRUSH BRUSH 00 16 Figure 19.

29 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 20. Gray vuggy silica rock with abun- dant voids after plagioclase and pyroxene phe- nocrysts in andesite flow. From Superior quarry.

AB Figure 21. A, Enargite crystals in vug and groundmass (gray areas) of vuggy silica rock. Largest crystal is about 5 mm wide. B, Back- scattered SEM image of enargite and pyrite crystals in vuggy silica alteration. Samples from Superior quarry.

Figure 22. Small dark gray enargite crystals filling funnel-shaped feature (hydrothermal vent?) in white chalcedonic silica, Superior quarry. Cluster of enargite crystals is about 8 mm wide.

30 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 23. Tan chalcedony replacing relict flow and devitrification layers in dacite flow. Gray areas are hematite after pyrite. Sample is about 15 cm wide. From the Superior quarry.

Figure 24. Massive tan chalcedony cut by hydrothermal breccias with sulfide minerals in gray areas. From the Superior quarry.

Figure 25. Steeply dipping, quartz-bearing felsic dike cutting dacite in the southwest highwall of the Superior quarry. Dike forms light-colored rocks in the center of the photo (between red lines).

31 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 26. Hydrothermal breccia with clasts of early stage white chalcedony in tan to gray chalcedony with sulfide minerals in gray areas. From the Superior quarry.

Figure 27. Sulfide mineral-bearing hydrother- mal breccia developed in massive tan silicified rock in the Superior quarry.

Figure 28. Massive tan silicified dacite tuff(?) cut by stockwork of sulfide mineral-bearing gray chalcedony in the Superior quarry.

32 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 29. Brecciated, finely laminated, siliceous hydro- thermal sedimentary rocks in the southwest part of the Superior quarry (see fig. 19).

Figure 30. Fault breccia with clay-supported fragments that contains the highest gold content (1.7 ppm) in the Superior quarry.

Figure 31. North-striking fault with red clay gouge developed in massive vuggy silica rock in the Superior quarry.

33 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 32. Red to brown smectite clay zone developed from alteration of bedded tuff. Note faults on left and right sides that terminate bed- ding. From the Superior quarry.

Figure 33. Taugow from the Superior quarry. Outcrops near top of Taugow consist of aluniti- cally-altered tuff breccia. High ridge in back- ground is north of the White River Fault Zone and is underlain by the Oligocene Ohanapecosh Formation.

Figure 34 Knob of alunitic alteration on Taugow. Rocks are probably tuff and tuff breccia now replaced by pale pink alunite and fine-grained white silica. White River Valley in distance.

34 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 35. Leached silicified tuff breccia with relict pyroclastic textures exposed in roadcut near top of Taugow.

Figure 36. Narrow fine-grained silicic dike cut- ting silicified tuff breccia near top of Taugow.

Figure 37. Blocks of vuggy silica alteration in hydrothermal breccia near top of Taugow. Larg- est block shows relict flow banding or bedded tuffaceous texture. Breccia matrix consists of fine-grained silica and hematite.

35 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington N Pit Outline 300' --complex, multi-staged, silicified breccias of Scatter Creek_Hardie Silica (8.5 x11).dwg [Scatter Creek_Hardie Silica (8.5 x11).mcl] 10/9/2003 --primary host to massive hydrothermal breccias --local, vent related pyroclastics derived from a possible --felsitic, dike-like masses which cut outcrops of Unconformity Scale in Feet GENERALIZED GEOLOGY Major Faults 50' 100' 200' D hydrothermal origin. Breccias vary from massive, coarse heterolithologic Vent Facies Pyroclastics with a rock flour matrix. Fragments consist of Fifes Peak andesite, vent facies volcanic center to the west and south of the Hardie pit. These pyroclastics are one another indicating coeval formation. a altered to clays or silica depending on location in relation to hydrothermal vent zones. exposed in the Hardie pit. Although commonly strongly silicified, the Fifes Peak comprised of fragments of Fifes Peak andesite, dacitic flow dome material and (no recognizable phenocrysts), irregular dikes containing varying amounts of undefined ignimbritic material, ash and pumice. Pyroclastics are predominantly rounded hydrothermal breccia fragments. Lateral tendrils of the dike attenuate intrusions to fine grain "shatter" brecciation consisting of hostpyroclastics rock and fragments previous breccia stages. Various breccia stages often crosscut into, and intrude darker, massiveinto hydrothermal anastomosing, breccia milky and quartz often veins transform before terminating. massive, hydrothermal breccia. Strongly silicified, tan to buff, cherty textured is discerned by its uniformphenocrysts fine-grained have porphyritic been texture leached where leaving original equally plagioclase dispersed cavities. Hydrothermal Breccia Masses Felsite Porphyry Dikes? Fifes Peak Andesite Flows U 0 SCATTER CREEK QUARRY - PIT "A" (G. Heinemeyer, 2002) Lithology

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FIGURE 48 10

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1 Generalized geologic map of the Scatter Creek quarry. 010

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14750 14500 14250 0 14000 0 5 9 199 1 N N N N Figure 38.

36 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 39. Stockpile of sized silica at Scatter Creek quarry being loaded for shipment to James Hardie Building Products, Inc., for use in produc- ing fiber cement-based building products.

Figure 40. Gray vuggy silica replacing porphy- ritic andesite cut by white quartz and chalcedony veins and hydrothermal breccias. From the Scat- ter Creek quarry.

Figure 41. Voids developed in porphyritic andesite after leached plagioclase and pyroxene phenocrysts by acid hydrothermal fluids leaving a residual ground mass of silica. Tan chalcedonic veins cut the vuggy silica. Label is about 4 cm wide. From the Scatter Creek quarry.

37 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 42. Northeast-trending rib of orang- ish-brown vuggy silica alteration (VS) bor- dered by light-colored alunitic (AA) and illitic (I) alteration localized along fault zone in Scatter Creek quarry.

Figure 43. “Clay Hole” (fig. 38). South side of northeast- trending rib of vuggy silica alteration (fig. 42) consisting of reddish colored illitic alteration and pale green chlorite- montmorillonite-rich propylitic alteration that forms floor of the Scatter Creek quarry.

38 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 44. Oxidation in the Scatter Creek quarry. Leaching of hematite from vuggy silica in the near surface forms a white vuggy silica rock that is underlain by gray to brown vuggy silica with abundant hematite. Relict pods of pyrite-rich alteration indicate that hematite is replacing pyrite.

Figure 45. Vuggy silica cut by early stage of white chalcedonic hydrothermal breccia and veins. From the Scatter Creek quarry.

39 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 46. Vuggy silica in andesite cut by hydro- thermal breccias with tan chalcedony matrix and hematite after pyrite and associated chalcedony and quartz veins. From the Scatter Creek quarry.

Figure 47. Fracture in vuggy silica filled with late-stage hydrothermal red clay composed of hematite, smectite, and dickite and commonly hav- ing elevated concentrations of Au, As, Sb, and Hg. From the Scatter Creek quarry.

40 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 48. White outcrops of leached rock that formed in the near-surface steam-heated zone. Altered rocks in background are densely silicified and formed below the paleo ground water table in the upper part of the hydrothermal system. See figure 38 for outcrop location.

Figure 49. Map showing distribution of Osceola Mudflow and Paradise lahar (modified from Crandell, 1971, plate 3). Distribution of Osceola Mudflow in subsurface from Dragovich and oth- ers (1994). Distributions of tephra layers F and S (Mullineaux,1974) shown near Mount Rainier. Figure reproduced from Vallance and Scott (1997, fig. 1).

41 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 50. Dark-gray clay-pyrite rich matrix of the Osceola Mudflow near Greenwater. Orange color due to surface oxidation of pyrite that extends a few cm or less below the outcrop surface. Small white clasts are advanced argillic alteration.

Figure 51. Typical outcrop of the Osceola Mudflow along the White River near Green- water. Osceola Mudflow is about 8 m thick. The characteristic pale yellow color is due to surficial weathering of pyrite in clay-rich matrix. The Osceola Mudflow here overlies about 1 m of gray compact silt, sand and angular pebbles and sparse cobbles, which is a runout facies of lahars (LRO) that were associated with erup- tions at Mount Rainier between 6,000 and 6,400 radiocarbon years ago (6,700 and 7,400 calendar years B.P.). The gray LRO, in turn, overlies stream gravel (reddish-brown unit right at river level).

Figure 52. Typical smectite-pyrite alteration of andesite clast in the Osceola Mudflow near Gre- enwater. Clast has a narrow oxidation (weath- ering) rind surrounding rock with unoxidized disseminated and vesicle filling pyrite.

42 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 53. Back-scattered SEM image of smectite altera- tion of andesite clast in the Osceola Mudflow. Plagioclase phenocrysts are relatively unaltered.

Figure 54. Back-scattered SEM image of smectite-pyrite alteration of andesite clast in the Osceola Mudflow. Plagio- clase phenocrysts are relatively unaltered.

Figure 55. Back-scattered SEM image of alunite, opaline silica (SiO2), and pyrite in advanced argillic altered clast in the Osceola Mudflow.

43 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 56. Back-scattered SEM image of alunite, anhydrite/ gypsum, and pyrite in advanced argillic altered clast in the Osceola Mudflow.

Figure 57. Back-scattered SEM image of alunite contain- ing P-rich domains in advanced argillic altered clast in the Osceola Mudflow.

Figure 58. Back-scattered SEM image of intergrown alunite and kaolinite in advanced argillic altered clast in the Osceola Mudflow.

44 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 59. Back-scattered SEM image of vug-filling anhydrite/gypsum and fluorite in advanced argillic altered clast in the Osceola Mudflow.

Figure 60. Schematic diagram of stage height versus time (hydrograph) for mass flow at point in bottom of valley, and depositional sequence of flow illustrating incremental deposition model for explaining nor- mal grading. Deposition illustrated for two stations 1 and 2 at heights h1 and h2 above valley bottom and with ultimate thicknesses t1 and t2. Short dashed lines through hydrograph indicate uniform incremental deposition. Sense of motion of mass flow is to left. See text for explanation. Figure reproduced from Val- lance and Scott (1997, fig. 13).

45 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Figure 61. Exposure of Osceola Mudflow over- lying well bedded late Pleistocene glacial-fluvial deposits in the Corliss quarry. Note dark gray trees protruding from the center of the Osceola Mudflow. Figure 62. Partly charred trees protrud- ing from the Osceola Mudflow in the Corliss quarry. Note generally rounded cobbles up to 50 cm in the Osceola.

Figure 62. Partly charred trees protruding from the Osceola Mudflow in the Corliss quarry. Note generally rounded cobbles up to 50 cm in the Osceola.

Figure 63. Base of the Osceola Mudflow in the Corliss quarry. Note dark orange, iron rich hard pan forming beneath the Osceola and well rounded clasts in the Osceola.

46 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

Table 1. Hydrothermal alteration assemblages in the White River altered area defined by Portable Infrared Mineral Analyzer (PIMA) analyses.

Alteration type Mineral assemblage1 Occurrence (fi g. 8) Silica Quartz, cristobalite, and (or) Silicifi ed zones (fi g. 8), including vuggy chalcedony ± pyrite silica Alunite Quartz + alunite ± pyrite Silicifi ed zones and fringing silicifi ed zones (fi g. 8) Dickite Quartz + dickite ± pyrite Fringing silicifi cation Illite Quartz + illite + pyrite Fringing silicifi cation and transitional to propylitic alteration Kaolinite Quartz + kaolinite ± pyrite ± alunite Fringing silicifi cation Pyrophyllite Quartz + pyrophyllite + pyrite ± alunite Vug-fi lling and fringing silicifi cation Montmorillonite Montmorillonite/smectite + pyrite ± Recessively weathering, argillic and chlorite ± calcite propylitic alteration Halloysite Halloysite ± pyrite Late fault zone; hydrothermal breccia matrix Montmorillonite ± Montmorillonite/smectite ± dickite + Late Fe-rich clay-fi lled fracture and fault dickite hematite zones cutting vuggy silica 1Mineral assemblages defi ned on the basis of hand specimen identifi cation, PIMA analyses, and limited petrographic study. Nearly all samples probably had pyrite, but pyrite is oxidized in most samples.

47 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington chalcedony veins and breccias in drill holes quarry idespread W HS LS or late HS Widespread LS only Not present HS only Widespread LS, late HS Superior quarry and LS or HS Scatter Creek LS or HS Superior quarry uid

ared

, Sb, Ag vent) Hg, Tl, (Au, Ag if fl As, Au, Ag metals overprint steam- heated, As, Sb, Au Ag, if deep fl race Au, AgAu, race LS, mid to late T As, Sb, Se, Au, As, Sb, Se, Var. As Barren, or Cu, Hg, unless Hg if only cance Metals LS or HS White River

ow dation ores

ow

uid, boiling at depth;

pervasive fl cryptocrystalline at ~200°C fl (hydrologic) depression, focus of upfl to high-sulfi paleowater table distal from source Shallow portion of system, <200°Cm rapidly cooling Permeable core, principal host Paleowater table, may be massive <150 m depth m hydrothermal system to 1-2+ km from source dation. >150 m >200°CAg, base Au, Only at surface Paleosurface, topographic Shallow depth, <150 In vadose zone Steam-heated origin, above Core of volcanic- At water table, up

uid

2 ow 2

dation; HS, high sulfi

uid, colloids;

solution pH<2, >95 percent SiO pH ~2-3, 80-90 percent SiO hot springs recrystallized from gel from steam-heated zone; deep fl may contribute to outfl fl Extreme leaching at Moderate leaching, From low-T From low-T ypes of silicic alteration in the White River altered area (modified from Hedenquist and others, 2000, table 4). ype Formation Where? Signifi T T cation From cooling water Surface to 500 m,

(vuggy quartz) (opaline) colloform bands; cryptocrystalline veins Quartz veins, vugs From cooling Residual silica Residual silica Sinter pH From near-neutral Silicifi Chalcedony horizon Silica remobilized Chalcedony veins, able 2. Abbreviations: LS, low sulfi T

48 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

49 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

50 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

51 Field Guide to Hydrothermal Alteration in the White River Altered Area and in the Osceola Mudflow, Washington

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